Note: Descriptions are shown in the official language in which they were submitted.
~ ~57~10~
PROCESS FOR ISOLATION OF PROTEINS
_ROM PLANT LEAVES
FIELD OF T~IE INVENTION
In a broad aspect this invention relates to a pro-
cess for isolating proteins from plant leaves. In another
aspect it relates to a process for obtaining ribulose 1,5-
diphosphate carboxylase from the green leaves of p:Lants. In
another, and more specific aspect, it relates to a process
for obtaining ribulose 1,5-diphosphate carboxylase from to-
bacco leaves.
BACKGROUND
The succulent leaves of certain plants, includingtobacco, spinach, soybeans, wheat, cotton and alfalfa, are
composed of 10-20% solids, the balance being water. For its
parts, the solid portion is composed of a water soluble por-
tion and a water insoluble portion, the latter being made up,
for the most part, of the fibrous structural material of the
leaf.
11 ~ S7~J7
The water soluble compounds are divisible into two
groups. One group includes compounds of relatively lower
molecular weight such as sugars, vitamins, amino acids and
other compounds whose molecular weight do not exceed about
10,000. The second group is almost exclusively proteins whose
molecular weights are about 30,000 ox greater.
The proteins can be resolved into two fractions. One
fraction contains a mixture of proteins whose molecular weights
range from about 30,000 to 100,000. These proteins are some-
times referxed to as "Fraction 2 pro~eins." The remain:ing
fraction comprises a single protein having a molecular weigh~
of about 550,0Q0 and is some~imes reLerred to as 'IFraction 1
protein."
Fraction 1 protein was first identified in 1947. Sub-
sequent research led to the discovery that this protein was an
enzyme invol~ed in photosynthesis. Sinc~ then it has been given
a number of names. ~mong these are ribulose 1,S-diphosphate
carboxylase, carboxydismutase, ribulose l,~bisphosphate carboxy-
lase and ribulose 1,5-di(or bis) phosphate carboxylase-oxygenase.
~ raction 1 protein may compose up to 25% of the total
protein content of a leaf and up to 10% of the solid matter in
the leaf. In 1970 it was discovered that crystalline Fraction 1
protein could be obtained from tobacco leaves.
Fraction 1 protein, when pure, is o~orless~ tasteless
and colorless and has high nutritional value. In view of these
properties, and because it can be obtained in high purity,
Fraction 1 protein is considered to have a poten~ially valuable
application as a food supplement for animals and humans. In the
case of humans, the additive could be a component of high protein
or other special diets. It has, for example, been suggested as
a supplement to the diet of persons who require dialysis bec~use
of kidney disease.
~ ~57~
Despite its relative abundance in cultivated plants,
Fraction 1 protein is not a commercially im~ortant product
since the processes known to the ar~ ror obtaining it rom
vegetable matter are not commercially feasible.
Three basic processes for isolating Fraction 1 pro-
tein ha~e been described in the published literature. Ea~h
published method begins with pulping the leaves, or leaves and
stal~ of the plant, followed by expressing a green juice from
the pulp. The green juice, which contains finely particulate
green pigmented material, is clarified for example, by filtra-
tion or centrifugatlon, to separate the finely particulate
solid matter from the liquid. The resulting liquid is brown
in color.
The first method descxibed for isolating Fraction 1
protein invol~ed concentration of Fraction 1 protain simultan-
eously wi~h its partial separation fxom lower molecular weight
compounds in the brown juice by molecular filtration. Using a
molecular sieve whose pores would pass smaller molecules with-
out passing Fraction 1 protein, the brown juice was placed
under pressure so that small molecules would pass through the
pores.
The solution containing the Fraction 1 protein was
concentrated about ten fold and then dialyzed to remove addi-
tional small molecules in the solution~ Dialysis was accom-
plished using a collodion type dialysis bag. The pores of
the bag would not permit pa~sage of ~he Fraction 1 protein
but allowed the smaller molecules to escape through the bag
into water. During dialysis, crystals of Fraction 1 protein
formed.
1~7~r~
The secon~ method developed to isolate the Fraction
1 protein involved passing the brown j uice ob~ained from the
12aves through a Sephadex chromatographic column. S~phadex
~.k ~
consists of water insoluble ~icroscopic beads of polymeri~ed
sugar. Either Sephadex G 25 or G-50 was used to perform the
separation. Selection of proper ~eads permits ~mall molecules
to ~enetrate to the interior of their structure to the exclu-
sion of larger molecules. The laxger molecules, therefore,
are only found in the ll~uid in the interstices between the
tightly packed Sephadex beads. This lnterstitial space .is
referred to as the "void volume".
To achieve effective separation, the volume of brown
juice cannot exceed about 25% o~ the total volume of the beads.
The beads are first equilibrated with a buffer and a volume of
brown juice, containing the same buffer, is then layered on top
of the Sep~adex column.
The brown liquid is eluted from the column using the
buffer solution. A~ the juice moves do~n ~he column, the pas-
sage of small molecules is retarded si~ce ~hey penetrate the
interior of the beads. The large Fraction 1 molecules, on the
other hand, move at a faster rate down the column through the
labyrinth formed by the interstices between the beads and
emerges from the column as a clear brown solution. However,
elution results in at least two-fold dilution of the solution.
Removal o~ the smaller molecules changes the environment around
the molecules of Fraction 1 protein which leads to crys~alliza-
tion.
le ~rK
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~s7~r3~
The most recently described method provides passage
of the brown juice through a Sephadex G-25 column as described
above. If Fraction 1 protein does not crystallize, as is the
case with the extract of all plants except tobacco, ammonium
sulfate is added until the solution is 30-50% saturated. This
leads to precipitation of an amorphous material which is col-
lected by centrifugation. After separation, the precipitate
is redissolved in a smaller volume of buffer than that from
which it was precipitated to which is added 8% polyethylene
glycol. This mixture is placed in an open dish adjacent to an-
other open dish containing silica gel and the two dishes con-
fined in a closed vessel. Water is gradually evaporated from
the protein solution and absorbed by the silica gel. With the
passage of time, crystals of Fraction 1 protein develop.
It will be clear to those skilled in the art that
the prior art processes described above are either time consum-
ing, expensive or both. However, in our United States Patent
No. ~,268,632 we describe a simple process for isolating Frac-
tion I protein comprising the steps of converting the leaves to
a pulp, heating the liquid portion of the pulp to a temperature
below that which causes the protein to denature followed by
cooling the liquid portion to a temperature at which Fraction 1
protein, i.e., ribulose l,5-diphosphate carboxylase crystal-
lizes.
SUMMARY OP THE INVENTION
Since making the invention described in our United
States Patent No. ~,268,632, we have discovered an even simpler
and more efficient process for isolating ribulose 1,5-diphosphate
carboxylase from the leaves of green plants. In that regard~ we
~1
; ~ 5~r~'~
have discovered that the heating step which we originally be-
lieved to have been an essential part of the process can be
eliminated in most cases. By our improved process, ribulose
1,5-diphosphate carboxylase is obtained in crystalline form by
adjusting the pH of the liquid portion of a pulp derived from the
leaves to a value in the range of from between about 6 to a pH
above that at which the protein will denature and precipitate as
an amorphous mass, i.e., to a value above the isoelectric point
which occurs at about pH 5Ø The liquid, after separation of
insoluble material, is then permitted to stand, preferably while
cooled below ambient temperature, to permit crystallization of
the Fraction 1 protein. It has been our general observation
that crystallization occurs more readily as the pH decreases,
i.e., nears the isoelectric point.
An object of this invention is to provide an improved
process for the isolation of Fraction 1 protein.
Another object is to obtain Fraction 1 protein in high
yield and purity.
According to the present invention, there is provided a
process for obtaining ribulose 1,5-diphosphate carboxylase from
plant material comprising the leaves of green plants which
process comprises the steps:
a) converting the leaves to a pulp comprising a mixture of a
solid portion and a liquid portion, said liquid portion contain-
ing dissolved ribulose l,5-diphosphate carboxylase;
b) adjusting, if necessary, the pH of the liquid por-tion to
within the range of pH 6.0 to a pH sufficiently above the iso-
electric point of the proteins in the liquid portion that said
proteins do not precipitate;
c) separating the liquid portion from the solid portion; and
d) storing said liquid portion at a temperature at which said
ribulose 1,5-diphosphate carboxylase crystallizes;
-- 6 --
e) separating crystals of ribulose 1,5-diphosphate carboxylase
from the liquid portion.
The present invention also provides ribulose 1,5-diphos
phate carboxylase in the form of octagonal crystals.
The manner in which these and other objects are accom-
plished by the present invention is described in the following
detailed description o~ the invention.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention may be used to
isolate ribulose 1,5~diphosphate carboxylase and lower molecular
weight protein from leaves of many varietiesA However, because
tobacco leaves, and particularly the leaves of imma~ure tobacco,
are a particularly rich source of the protein, it is preferred
to use such leaves in the process of the invention. Accordingly,
the invention will be described witn speci~ic reference to the
isolation of ribulose l,S-diphosphate carboxylase from tobacco.
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~ ~7~
After detachment of the leaves from the tobacco plant,
the leaves, or leaves and stalk toget~er if small plants are the
source of the leaves, are ground, crushed or otherwise reduced
to a pulp to release the li~uid portion of the leaves from the
solids. Preferably, the pulping process is carried out in the
presence of a reducing agent. In that regard, the pulping pxo-
cess permits phenol oxidase e~zymes present in the leaves to
contc~ct the leaf proteins. This results in oxidation of aromatic
amino acids such as tyrosine which comprise part of the primary
structure of proteins. This oxidation modifies the protein,
made visually manifest by their becoming brown, and lowers their
solubility in water. The reducing agent, in effect, acts as an
antioxidant to suppress this oxidation.
The presently preferred reducing agent for use in the
invention is 2-m~rcaptoethanol because it is ~olatile and evap-
orates duri~g the further processing described below leaving
little or no residue in the material isolated. ~owever, other
reducing agents may also be used. Among these are agen~s such
as sodium metabisulfite and dithiothreitol. Separation of the
residue of these agents, if any, can be done using conventional
techniques. The amount of reducing agent suXficient to control
the oxidation can vary depending, for example, on the agent
selected~ In the case of 2-mercaptoethanol, effective su~pres-
sion o the undesirable oxidation can be achieved using about
5 milliliters of the liquid agent per kilogram of plant material
being processed~
The liquid portion of the plant material contains the
plant proteins, includinq Fraction 1, and other solids in dis-
solved for~O Th~ solid portion of the pulp includes coarse,
easily separated material and finally particulate gxeen pig-
mented material which is difficult to separate from the li~uid.The coarse material is preferably separated from the liquid por-
tion promptly arter the leaf material is converted to a pulp. A
simple filtration, for example, using cheese cloth, will accom-
plish this separation. When this is done, the liquid portion
which still contains the finely particulate, green pigmented
material is treated with acid, preferably hydrochloric acid, as
necessary, to bring the pH to within the desired range, i.e., to
within the range from about p~ 6.0 ~o a point near but above the
isoelectric point at which the protein i~ the liquid portion is
denatured whereby it precipitates as an amorphous mass. This
mass co~ains both ~raction 1 and Fraction 2 protein ma~erial.
The isoe}ec~ric poin~ of proteins is at about p~ 5Ø Thexe~
fore, the practical lower limit ~o which thP pH should be ad-
justed according to the present invention is about pH 5 . 3 .
Separation of the coarse ~aterial may be carried out a~ter
acidification of the liquid. Other mineral acids including
phosphoric and sulfuric may also be used.
We have found thal~ the pH of the liquid portion of
tobacco leaf pulp varies according to the age of the plant.
In ~he case of ~ery young plants, i.e., plants less than about
12" tall, the pH will be in the range of about 6.0 or higher.
As the plants mature, the pH of the liquid portion decreases,
i.e., the liquid portion is na~urally more a~idic. For exam-
ple, the pH of liquid from plants in the range Oc from 18" to
24" in height was about pH 5.7, whereas the liquid portion
derived from plants 24" to 36" had a p~ of about 5.3.
For best results, preferably the pH o' the liuid por-
tion is adjusted to a range from about 5.4 to 5.8, most prefer-
ably to a pH of about 5.4-5.6. When the pH is above about 5 . 8,
crystallization occurs at a significantly slower rat~ than at a
lower p~. By contrast, when ~he pH is adjusted to below about
-8~
I ~S7~0~7
;.4, the Fraction 1 protein which is obtained has lost desirable
properties. ~e believe that adjusting the p~ to near the iso-
electric point causes changes in the Fraction 1 protein akin to
those which result from its denaturation. For example, it is
more difficult to xedissolve Fraction 1 protein which crystal-
lizes from a liquid at pH below about 5.4.
We have also found that by adjustment of the pH to
within ~he preferred range 5.4-5.6, the separation of the finely
particulate green material is facilitated as i~ partially coagu-
lates. This material, which contains the plant chlorophyll, can
be separated by any sui~a~le means but centxifugation is a con-
venient and preferred way to do so.
In ~ome cases, particularly in the case of pulp ma~er-
ial from more mature plants or if a pH above about 5.6 is used,
it may be ~ecessary to heat the mixture containing finely par-
ticulate green material to obtain easy separation. The heating
step has the effect o~ coagulating the finely particulate mater-
ial to an extent that permits its separation by centrifugi~g as
discus~ed above.
The entire pulp may be heated to acilitate separa~ion
of the green finely particulate material. However, it is pre-
ferred to heat the portion of the pulp remaining after the coarse
material is removed.
The heating step must be carrie~ out at a temperature
below that at which the protein will denature by heat alone.
Generally, therefore, the heating step should be carried out
below about 5~C as heating above that temperature results in
precipitation of the protein. We have obtained good results
by heating the pulp to about 48C (118F) for not more than
about lS minutes. Temperatures below about 48C can be used
but longer heating times are required.
_g_
l 1 5'~
The heat treatment can be performed either as a con-
tinuous or batch process as described in OUI' United States Patent
No. ~,268,632. Thus, in a batch process, the pulp is placed in a
vessel whereby heat is transferred to the pulp under conditions
where no part of the pulp, or at least the liquid portion there-
of, is heated to a temperature at which the protein denatures.
As indicated above, preferably the pulp is heated to a tempera-
ture of 50 ~ 1C for from about 15 minutes to about 20 minutes.
In a continuous process, the pulp is pumped without
undue agitation through coils immersed in a liquid heated to
a temperature such that, by heat exchange~ a specified volume
of pulp would be heated to 50C ~ 1C for from about 15 minutes
to about 20 minutes and then through coils in contact with liq-
uid at a temperature lower than 50C to reduce the temperature
of the pulp.
Heating the pulp as described above to cause coagula-
tion of the finely particulate material is more efficient than
merely adjusting the pH. However, the heating regimen should
be used only if necessary to remove the finely particulate mate
rial since it has the actual effect of increasing the time over
which crystallization of the Fraction 1 protein occurs and, in
some cases, the amount of protein obtained.
As indicated, the finely particulate material can be
separated after coagulation, for example, by centrifugation,
from the liquid portion. The supernatant liquid obtalned is a
brown juice. This juice is stored at a temperature at which
crystallization will occur, usually at or below room tempera-
ture to obtain crystals of Fraction 1 protein. We have ob-
tained particularly good results by cooling the brown juice to
about 8C. The maximum storage time required is not more than about
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~ ~57~0~
16 hoursO It has been our experience that storage beyond 16
hours does not usually improve yields. The crystallized ri-
bulose l,5-diphosphate car~o~ylase is separated fxom the super-
natant liquid by filtration or centrirugation (3000 ~M, 5 min.).
The crystalline form of ribulose 1,5-diphosphate
carboxylase differs from the three forms obtained using prior
art processes. Form T crystals have ~he shape of dodecahedrons
and are produced by the previously mentioned processes using
molecular sieves or Sephadex chromatography. Form II crystals
have the shape of extremely thin plates and so far have been
produced only under very special conditions and in extremely
s~all amounts for x-ray crystallographic studies. Form III
crystals are tetragonal bipyramlds and are produced by the
ammonium sulfate and polyethylene glycol treatment previously
mentioned.
By contrast, the Fraction 1 protein crystals produced
by the prooess described herein take yet a fourth form, unlike
the other three forms of crystals known to the art. Thus, using
~he process of ~he present inven~ion, Fraction 1 protei~ crys~als
are obtained ha~ing an apparent octagonal form, by microscopic
examination, in high yield and in high purity.
In contrast to Form I crystals which will redissolve
in water containing comm~n salt (NaCl), the octagonal crystals
remain undissolved but will generally go in~o solution when the
crystals are suspended in water adjus~ed to pH 7.5 or higher by
sodium hydroxide (NaOH). We have ~ound that the protein ob
tained from very mature plan~s, i.e., ~hose ~4'' to 36'1 in heigh~
whose brown juice has a pH of 5.3 naturally, may not redissolve
in water (pH 8.i by ~he addition of NaOH). Dialysis of the re
dissolved Fraction 1 protein against a buffer (tris, pH 7.5~
--11~
1 ~7~0~
followed by passage through a Sephadex column will cause re-
crystallization, but now as Form I crystals.
The Fraction l crystals obtained from the brown juice
can be conveniently purified by washing with water to remove
contaminants. Separation of the crystals fxom the supernatant
is again be~t achieved by centrifuging. Low speed centrifuga-
tion (~ 3,000 RPM) for five minutes will suffice.
This process Qf crystallization of the Fraction l
protein will result in its ~ubstan~ially complete removal
~rom the brown juice. The resulting supernatant contains
Fraction 2 proteins, other soluble solids and uncrystallized
Fractiorl 1 protei~, if any. Fraction ? protein may be removed
from the supernatant by acidifying it to at or below the iso-
electric point, i.e., to a pH of 5.0 or below. This causes
the proteins in solution to precipitate. Highest yields o
protein are obtained by adjusting the p~ to about 4.0-4.5 by
the addition of hydrcchloric acid or other suitable acids.
The resulting precipitate can be collected by centrifugation
(3000 RPM, S min.). Contamin~nts can be removed if the pre-
cipitate is washed with water and again collected by centri-
figuation.
The passage o tim~ b~tween harves~ing the leaves,
converti~g them to a pulp (which may be by grinding, crushing
or any other suitable process), adjusting ~he pH, performing
-12-
t ~ s ~
the heating ste?, if necessa~J, and separation of solid material
from the liquld portion should be accomplished as soon after
harvesting as possible. Delays in accomplishing these steps re-
duces the yield of ribulose 1,5-diphosphate carboxylase that can
be obtained. Therefore, it is preferred to perform these opera-
tions at or near the site where the leaves are harvested.
The following examples provide further details of the
invention.
EX~MPLE 1
Type NC95 tobacco plants are cultivated at a plant
d nsity of 0.5 square feet per plant until a height of 18-24
inches is attained. The plants are cultivated in such a way
that the leaves are deep green in color. The entire aerial
portions of the plants are harvested and cut into pieces
small enough to be introduced into a one gallon size Waring
blender. The blades of the blender are covered with about
200 ml. of water. (The Waring blender will not disintegrate
the plant material unless the blades are submerged in a
liquid. However, with other such devices, such as a Rietz
disintegrator, addition of water would be unnecessary.)
A one kilogram batch of coarsely chopped stems and
leaves obtained from the harvested plant material is added
to the water with 5 ml~ of 2-mercaptoethanol and blended to
a smooth pulp. The resulting pulp, which has the consistency
of a thick pancake bat~er, consisting of a volume of about
1.2 liters. The coarse material in the pulp was poured onto
two layers of 24/20 mesh cheese cloth supported on a 8 inch
diameter, 32 mesh sieve whi-ch is placed in a large funnel
draining into a collecting flask.
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~ ~L57~
Processed in this way, the 1.2 liters of pulp yields
approximately 1.0 litex of liquid containing green pi~mented
material. The "green juice" had a pH of from about 5.7 to 5~9
in different preparations.
The green juice was divided into equal aliquots of
500 ml each. One aliquot was kept at 25C while the other was
heated to 50C for 10 minutes. Then both aliquots were simul~
taneously centrifuged in a Beckmann Ultra Centrifuge in an
R-21 ro~or at 18000 RPM for 30 minutesO This high c~ntrifugal
force removed all of the green color as a precipitate leaving
a clear "brown ~uice". Each aliquot of brown juice, i.e., the
h~ated and unheated aliquots,-was divided into equal parts,
one part stored at 8C and the other allowed to stand at 25C.
Equal amounts of Fraction 1 protein crys~alli~ed from each
aliquot. Crystallization was complete in all cases within 1~
hours, alt~ough crystals appeared more rapidly where the brown
juice was refrigerated. This example demonstrates that heating
of the li~uid portion was not essential to obtaining the
crystals o ribulose 1,5-diphosphate carboxylase.
EX~MoeLE 2
Using the procedure of Example 1, a green juice having
a pH of 5.7 was obtained from tobacco plants 18" to 24" in
height. The green juice was divided into two equal portions.
The pH of one portion was adjusted to pH 6.2 using sodium
hydroxide. Both portions were heated to 50C for 10 mlnutes to
facilitate removal of the finely particulate green material
using moderate centrifugation. After removal of the green
material, the two samples o~ brown juice were stored at 8C.
-14-
1 1~7~r)~
Within a few hours, crystals appeared in the brown j uice of
pH 5 . 7 . No crystals appeared in the sample having pH 6 . 2
even after 24 hours.
In a similar experiment, brown ~ uice derived from
tobacco plants 24" to 36" in height having a pH of 5.3 pro-
duced crystals within 30 m1nutes and complete crystallization
occurred within 3 ho~s after the first appearance of crystals.
However, the resulti~g Fraction ~ protein would not redissolve
at pH 8-8 . 5 . In another experiment using tobacco plants 18"
to 24'1 in heigh~ whose brown liquid was pH 5.8, crystals of
Fraction 1 protein did not appear for 12 hours. Crystalliza-
tion was complete within 16 hours. These data demonstrate
that formation of crystals of Fraction 1 protein occurs more
rapidly at lower pH.
EX~MPLE 3
Using the process of Example 1, a green juice was
obtairled from very young tobacco plan~s less than 12 " tall.
The juice obtained in this way had a pH of 6Ø The total
juice obtained was divided into two equal parts and each
part was subdivided into four equal aliquots for further
processing. One aliquot from each of the original parts
ha~ing a pH of 60 0 served as a control. An aliquot from
each p æt was treated with hydrochloric acid to obtain a
pH of 5. 8; ano~her was adjusted to pH S. 6 and another
ad justed to pH 5. 4 . The four aliquots of one part were
heated to 50C for 10 minutes. These four aliquots and
the four aliquots ~rom the other part were centrifuged to
separate the finely particiilate green material.
1 1 5 ~ 7
All the aliquots were permitted to stand at 8 C to
permit the formation of crystals of Fraction 1 protein. The
time when crystals first appeared was noted and, when crystal-
lization was complete, the amount of crystals obtained was
noted. The brown juice was analyzed spectrophotometrically
to determine the amount of finely di~ided green particulate
matter contaminating the brown juice. The results are in
Table I below.
Table I
mg/ml of
g~ml of Crystals
Hours Before Green of Protein
Condition of pH of Green Appearance Material in From Brown
Green Juice Juiceof CrystalsBrown Juice luice
Not heated 6.0 8 10 6
" 5.8 6 5 6
" 5.6 3 1 6
" 5-4 3 0 6
Heated to 50C 6.0 48 0 3
" 5.8 48 0 3
" 5.6 16 0 5
" 5.4 3 0 6
These data further demonstrate that heating is not
required to cause crystallization of Fraction 1 protein but, ;
in fact, retards the rate of crystallization and decreases
the amount of protein obtained in most cases. The effect of
decreasing the pH is to clearly increase the rate at which
crystallization occurs. Furthermore, whereas heating the
samples facilitated the separation of the finely particulate
green material, complete separation of the green material
occurred for unheated samples whose pH had been adjusted to
pH 5.4-5.6.
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1~ :
~ ~7~1~7
We have determined the efficiency of separation of
Fraction 1 protein from green juice whose pH has been adjusted
to the desired range by comparing the Schlieren patterns obtained
from analytical centrifugation of the green juice and the brown
juice after crystallization of the Fraction 1 protein. The
former shows two well resolved peaks, one of which correspands
to Fraction 1 protein and the other to Fraction 2 proteins. In
the latter, only a single peak corresponding to Fraction 2
proteins is observed. Since the analytical centrifugation
method is capable of detecting as little as 0.1 ms~ml of ~rac~
tion 1 ~rotein, it can confidently be stated that, after
crystallization is complete, the concen~ration o Fraction 1
protein remaining in solution is less ~han 1%. ~y contrast,
the mother liquid obtained from the prior axt chromatography
process using a Sephadex column contained, in addi~ion to
Fraction 2 proteins, about 30~ of uncry~tallized Fraction 1
protein.
From t~e foregoing description, it can be seen that
the present invention provides a convenient process for obtain-
ing protein, and especially Fraction 1 protein, from plant
material. Thus, the process of the present invention obviates
the need for costly and elaborate molecular filtration and
Sephadex column5 as required by prior ar~ processes. ~'urther-
more, no ch~mical agent is required other than the reducing
agent which, in the case of 2-mercaptoethanol, evaporates
during processing or is dxiven off in the hea~ing step if used,
in order to obtain the Fraction 1 protein and the acid used to
adjust the pH of the liquid. Because it is unnec~ssary to
dilute the liquid, recovery~of Fraction 2 proteins is also
slmplified. Finally~ after remo~al of the Fraction 2 proteins
w17--
1 ~57~7
and uncrystcallized Fraction 1 protein :Erom the liquid portion, the liquid
portion still contains low molecular weight compounds of value that can be
more economically recovered than would be the case using the residue obtained
by prior art processes since they are in their natural form and undiluted.
By contrast, the residues obtained from prior art processes are contaminated
by the chemicals used in the process and have been diluted during separation
of the Fraction 1 protein which complicates further recovery. Our improved
process also makes it unnecessary in most cases to use the heating regimen
described in our United States Patent No. ~,268,632.
The invention has been described in terms of presently preferred
embodiments. However, from the foregoing description of the invention, those
skilled in the art will appreciate that modifications of the process can be
made without departing from the scope of the invention which is to be limited
only by the appended claims.
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