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accompanied by the last portions of protoalbumose, and then precipitated
the fraction of deuteroalbumose left alone in solution by saturation with
ammonium sulphate.

Kiihne and Chittenden had already got round this difficulty of isolating
deuteroalbumose by treating a dried mixture of the albumoses, such as is found
in Witte's peptone, with neutral and saturated solution of sodium chloride.
Here the deuteroalbumose only passes into solution. Although the proto-
albumose Avould only be partially thrown out of solution by saturating with
sodium chloride, yet it- has not the power when dry to pass into solution
in such a solvent. Witte's peptone is, however, a variable mixture, and
Neumeister, working with other samples, was unable to reobtain Kiihne and
Chittenden's result ; it may be that they were working with a sample
containing little or no protoalbumose.

Neumeister effects the separation as follows : —

The faintly acid solution is saturated with ammonium sulphate, and so
separated from peptones. The precipitate is dissolved by the addition of
water, separated from the excess of the salt by dialysis, and then the neutral

'^Ztsclir.f. Biol., Miinchen, 1887, Bd. xxiii. S. 381 ; ihid., 1888, Bd. xxiv. S. 267 ; ibid.,
1890, Bd. xxvi. S. 324.



CLE A VA G E THE OR Y OF PR O TEW DIGESTION. 4 1 3

solution is precipitated by saturation with sodium chloride, so throwing out
all the heteroalbumose and part of the protoalbumose which are separated
by dialysis. In the filtrate from saturation with sodium chloride in neutral
solution are the remainder of the protoalbumose and the whole of the deutero-
albumose ; to this, acetic acid solution, which has been saturated with sodium
chloride, is added, till a small portion filtered through a dry filter paper no
longer gives a precipitate with copper sulphate solution. ^ The mixed pre-
cipitate of jyroto- and (ieM?'eroalbumoses is now filtered off', and deuteroalbumose
is isolated from the filtrate by neutralising, dialysing off' the sodium chloride,
and precipitating by saturating with ammonium sulphate, or by adding excess
of alcohol.

This method of separating the albumoses may be shown schematically

thus : —

Mixed Albumoses
(saturated with sodium chloride in neutral solution) give



Heteroalbumose and Protoalbumose Protoalbumose and Deuteroalbumose
(Precipitate). (Filtrate).

On dialysis, the solution of these two On adding acetic acid in saturated sodium
gives chloride, this solution gives



Heteroalbumose Protoalbumose Protoalbumose and Deuteroalbumose

(Precipitate). (Solution). Deuteroalbumose (dialysed and pre-

(not further treated) cipitated by alcohol)
(Precipitate). (Filtrate).

Neumeister also tested the action of hydrolysing agents on pure proto- and
/ie^eroalbumoses prepared as has just been described. He showed that boiling
for three-quarters of an hour with 5 per cent, sulphuric acid was sufficient
to convert protoalbumose into deuteroalbumose accompanied by some peptone.
This was shown by the absence of turbidity on dialysis after neutralising
(absence of heteroalbumose), by saturation in neutral solution with sodium
chloride causing no precipitate (absence of protoalbumose), and by precipitation
occurring on making the saturated solution in sodium chloride acid with acetic
acid (presence of deuteroalbumose). In a similar fashion the conversion of
heteroalbumose into deuteroalbumose, by boiling with acid, was demonstrated ;
here a considerable formation of antialbumid was observed during the process.
On peptic digestion proto- and heteroalhwiaose each yielded a deuteroalbumose,
but they behaved differently towards trypsin. In the case of heteroalbumose,
a specific point could easily be determined, in the course of digestion with
trypsin in 0*2 per cent, sodium carbonate solution, when, in the presence of a
considerable quantity of peptone, only deuteroalbumose was present ; on the
other hand, deuteroalbumose could not be obtained in large quantity by the
action of trypsin on protoalbumose ; the products obtained were chiefly amido-
acids accompanied by a little peptone, this being probably due to the ease
with which the deuteroalbumose formed from protoalbumose undergoes decom-
position.

Neumeister confirms the results obtained by Kiihne and Chittenden, that
heteroalbumose is principally an antialbumose, but has some hemialbumose
mixed with it, while the composition of protoalbumose is the exact reverse,
it being essentially a hemialbumose, always accompanied, however, by some
antialbumose. The yield of unalterable peptone was, however, so small in
some experiments as to induce ISTeumeister to believe that perfectly pure proto-
albumose would contain only hemi groups, or, in other words, be completely
convertible by tryptic digestion into amido-acids. The deuteroalbumose

' This is a much more delicate test for protoalbumose (given by 1 in 5000) than acetic
acid and saturated sodiiun chloride solution (1 in 2000),



414



CHEMISTRY OF THE DIGESTIVE FROCESSES.



formed from protoalbiimose and that from heteroalbiimose are distinct bodies,
being distinguished by the fact that the deutero-comjDonnd formed from
protoalbnmose is to some extent sokible in saturated solution of ammonium
sulphate.^

Starting with fibrin, and forming albumoses from it both by the
action of acids and by peptic digestion, jSTeumeister also showed that in
order of time proto- and 7iefo?'oalbumoses first appeared, to be followed
later in the process by cleuterod,Vo\nn.o^Q.

Fibrin was boiled for three-quarters of an hour with 1 per cent,
sulphuric acid, after which the fluid was neutrahsed, and the neutralisa-
tion precipitate removed. In the filtrate both proto- and heteroalbu-
moses were found, but not a trace of deuteroalbumose ; the latter first
appeared after some hours' boiling, and by a continuance of the process
increased at the expense of the proto- and hetero-compounds so as to be
present finally in preponderating quantity.

In accordance with these experiments, Neumeister^ considers that
the peptic digestion of proteids takes place as represented in the follow-
ing scheme, in which the preponderance of any group is shown by a
dark line, while its presence in small quantity is signified by a hght
Kne: —

Proteid Molecule,
consisting of



Hemigroups



Protoalbumose
(Amphoalbumose)

I I

Deuteroalbumose
(Amphoalbumose)

I I

Amphojjeptone



Autigroups



Heteroalbumose
(Amphoalbumose)



Antialbumid



Deuteroalbumose Deuteroalbumose
(Ampboalbuinose) (Antialbnmose)

Amphopeptone Antipeptone



Tryptic Digestion of Proteids.

The proteolytic action of the pancreatic juice has not been known
for nearly so long a period as that of the gastric juice ; it was first
clearly proclaimed by Corvisart^ in 1857, although this author refers to
an earher statement, by Purkinje and Pappenheim in 1836, that extracts
of pancreas possess a dissolving action on proteids.

Claude Bernard * knew that pancreatic juice in the presence of bile
had the power of dissolving proteids, but stated that when alone it
had no such action, unless the proteid matter had previously been sub-
jected to the action of bile. This error was removed by Corvisart, who
clearly proved that pancreatic juice alone at the temperature of the



^ Ztschr.f. Biol., Miinchen, 1888, Bd. xxiv. S. 267.

^ Ibid., Muiichen, 1887, Bd. xxiii. S. 381. See also Ncumeister, '"Lelnbuch der
pliysiologischen Cliemie," Jena, where Keumeister concludes: — "The expression
hernipeptone has, according to this representation, only a theoretical meaning, and the
term hemialbumose corresponds to older notions and ought to be allowed gradually to
disappear from the text-books."

" "Collection de memoires sur une fonction pen connue du pancreas, la digestion des
aliments azotes," Paris, 1857.

•* "Lecons de physiologic cxperimentale," 1856, tome ii. p. 440.



CLE A VA GE THE OR Y OF PRO TEID DIGESTION. 4 1 5

body has a powerful digestive action on proteids in fluids of either
alkaline, acid or neutral reaction. In addition, he showed that infusions
of the fresh gland possess a sunilar action, that the active material
is precipitated by excess of alcohol and is dissolved again on the
addition of water to the precipitate, and that the activity of extracts
of the gland depends on the time after a meal at which the animal
is killed, being most active when a gland is extracted that has been
obtained from an animal killed six to nine hours after a full meal.
Corvisart also showed that the proteids are not merely dissolved, but
converted into substances possessing the same general characters as
those formed in peptic digestion.

These important results were denied at first by some observers, who
failed for some reason to obtain them on repeating Corvisart's experi-
ments, but were in the end abundantly confirmed by the researches of
Meissner,^ Danilewsky,^ and Klihne,^ and are now universally accepted.

Kiihne* not only confirmed the results of Corvisart, but made an
important advance, by showing that pancreatic juice owes its action to
an enzyme, to which he gave the name of trypsin. He next showed
that, although trypsin is precipitated by excess of salicylic acid, smaller
quantities of that substance do not stop the action of the enzyme,
while they do, as shown by Kolbe, stop the growth of organisms,
especially those concerned in putrefaction. Until this was ascertained,
digestion experiments with pancreatic juice w^ere complicated by the
putrefactive changes by which digestion was accompanied, for, while
trypsin acts in a neutral, and even in a faintly acid medium, its action
is stopped and the ferment gradually destroyed in a medium sufficiently
acid to stop the growth of bacteria by virtue of its acidity alone, so that
no one had been able to carry out prolonged experiments on pancreatic
digestion without the accompaniment of putrefaction. For this reason
it was unknown whether certain substances which appear towards the
end of the digestion were really due to the action of the enzyme or
were products of the putrefaction. Kuhne was the first to carry out
antiseptic digestion, and to show that these substances are really formed
by the agency of the trypsin; he also perfected a method of freeing
solutions of the enzyme from the products of proteid digestion, resulting
either from the self-digestion of the gland in the preparation of the
extracts or otherwise, thus clearing the way for a study of the various
products formed by the action of trypsin on proteids.

Instead of preparing a purified solution of trypsin, which is a
rather troublesome process, the power possessed by fibrin of absorbing
the ferment, as described in the case of peptic digestion, may be
utilised here also ; but if the digestion of coagulated proteids is to be
observed, a purified solution of trypsin must be first prepared.^

The first action of trypsin seems to be a simple solution of the
proteid which is undergoing digestion. This effect is most easily observed
if fibrin is the proteid undergoing digestion, when the coagulable proteid
present in the solution, just before the fibrin is completely dissolved, has

1 Ztschr.f. rat. Med., 1859, Dritte Eeihe, Bd. vii. S. 1.

^ Virchows Archiv, 1862, Bd. xxv. S. 279.

3/&^d, 1867, Bd. xxxix. S. 130.

■* Verlmndl. d. naturh.-med. Ver. z^i Heidelberg, 1877, N. F., Bd. i. S. 233.

''See Neumeister, " Lehrbuch der pliysiologischen Cliemie," Jena, 1893, S. 198;
K. Mann, "Ueber die Absorption der proteolytischen Enzyme durch die Eiweisskorper,"
Diss., Wurzburg, 1892, S. 23,



4 1 6 CHEMISTR Y OF THE DIGESTIVE PR O CESSES.

the properties of a globulin, but in the case of serum albumin no such
formation of a globulin takes place.^ If the proteid employed has
pre\dously been coagulated, no formation of a coagulable proteid is
observed, the first product being apparently deuteroalbumose.^

The appearances presented by proteid undergoing solution by the
action of pepsin and of trypsin respectively, are characteristically
different. In the case of pepsin and hydrochloric acid, the proteid
swells up, becomes transparent or translucent, and gradually dissolves ;
while, by the action of trypsin in alkaline solutions, the proteid does not
swell up or become clearer, but is attacked and eroded from the outside.

After being dissolved, the proteid is further attacked by the trypsin
and decomposed into various products, the final result being a certain
amount of peptone which is not further acted on, accompanied by
various nitrogenous bodies, of which those occurring in largest quantity
are two amido-acids, leucine and tyrosine.

The primary albumoses of peptic digestion are not found among the
intermediate products of tryptic digestion. No matter at what stage
digestion is interrupted, no trace of either jjroto- or heteroalbumose is
found ; the only albumose present is deuteroalbumose.^

Keumeister suggests that this may be due to the protoalbumose being
broken up as rapidly as it is formed into amido-acids, while the heteroalbumose
is immediately converted into deuteroalbumose. Be this as it may, the
experimental fact is, that neither protoalbumose nor heteroalbumose are
found at any stage of tryptic digestion.

According to ISTeumeister, the deuteroalbumose present is an anti-compound
not yielding any amido-acids when subjected to the further action of trypsin.*

Peptone is formed much more rapidly in tr}^tic than in peptic
digestion, the preliminary stages being apparently rushed through ; while
in peptic digestion scarcely any peptone is formed before complete
conversion into albumoses has taken place, and complete peptonisation
never occurs.

The most essential difference between the digestive action of trypsin
and that of jjepsin lies in the discovery of Ktihne, that the action of
the former enzyme does not cease with the formation of peptone, but
that ax3proximately one-half of the proteid, or of the peptone formed
from it, is converted into a number of cystalUne substances of much
simpler composition.

Not only does this take place in the direct tryptic digestion of proteids,
but if peptone formed by peptic digestion be submitted to tryptic
digestion, about one-half of it is decomposed in the above fashion. This
experiment led Kiihne to the cleavage theory, and to naming, on the
basis of this theory, the peptone of peptic digestion, am^j/topeptone ; the
peptone remaining after the completion of tryptic digestion, and which
is no longer affected by renewed digestion, cMl^^peptone ; and that
hypothetical substance which is supposed to form one moiety of the
amphopeptone, and be broken up by the action of the trypsin,

1 Keumeister, Ztsehr. f. Biol., Mlinchen, 1887, Bd. xxiii. S. 398 ; ibid., 1890, Bd. xxvii.
S. 311 ; Herrmann, Ztsehr. f. physiol. C/iem., Strassbur^;, 1887, Bd. xi. S. 521.

^ When trypsin acts in an alkaline medium, alkali albumin is first formed ; but this is a
very transient stage, the alkali albumin being quickly changed into deuteroalbumose.

^ Otto, Ztsehr. f. physiol. Chem., Strassburg, 1883, Bd. viii. S. 129; Neumeister,
Ztsehr./. Biol, Munchen, 1887, Bd. xxiii. S. 398.

•^Ztsehr./. Biol, Miinchen, 1887, Bd. xxiii. S. 381.



CLE A VA GE THE OR Y OE PR O TEID DIGESTION. 4 r 7

Acm-ipeptone. It will be seen from this that the term hemipeptone is
a term for something which has a separate existence only in theory.
There has as yet been no method either devised or fallen upon by
accident of separating these two substances which are supposed by the
cleavage theory to be present, mixed in equal proportions, in ampho-
peptone. This is somewhat remarkable, in view of the number of years
the theory has now been in vogue, and the large amount of experimental
work that has been carried out in connection with it, and ought to be
looked upon as an indication, either that amphopeptone is not really
a mixture of anti]oeptone with a hypothetical hemipeptone, but a
substance capable of breaking up under the action of trypsin into a new
peptone (antipeptone) and a number of amido-compounds ; or that anti-
and hemipeptones are not separately present in amphopeptone, but that
this peptone breaks up upon the further action of trypsin into antipeptone
and hemipeptone, and that this hypothetical hemipeptone is next acted
upon and broken into simpler bodies, finally yielding leucine, tyrosine,
and the other companions of antipeptone found in complete tryptic
digestion.

The decomposition of proteids by trypsin is represented by
Neumeister ^ according to the following schema : —

ProUicl.

I
Deiitei'oalbumose

Amphopeptoue



Antipeptone Hemipeptone



Leucine Tyrosine Aspartic Acid Tryptophan, etc.



According to the same author, several deuteroalbumoses are formed, in the
course of tryptic digestion, yiekling corresponding amphopeptones. He also
states that all the albumoses up to the present known, whether formed in
peptic or tryptic digestion, are amphoalbumoses, — that is to say, yield both
antipeptone and amido-acids on complete tryptic digestion. The ratio between
the amounts of antipeptone and of amido-acids is a very variable one ;
heteroalbumose, for example, yielding much antipeptone and little amido-acid,
while protoalbumose breaks up into much amido-acid and very little anti-
peptone. Those who hold the cleavage theory explain this by saying that
heteroalbumose is to a large extent an anti-substance, and protoalbumose
almost purely a hemi-substance ; but the experimental facts may be met
equally well by the statement, that heteroalbumose is an albumose of such a
chemical nature that it breaks up under the action of trypsin so as to yield a
large percentage of peptone unalterable by further action of trypsin, accom-
panied by a small amount of amido-acids ; protoalbumose is an albumose
different in nature from heteroalbumose, and yielding, on further tryptic
digestion, very little peptone (antipeptone) and a large amount of the amido-
acids. There is no more proof that either heteroalbumose or protoalbumose is
such a mixture of albumoses as the cleavage theory demands, than there is
that amphopeptone is such a mixture of the corresponding peptones.

All the observed facts of peptic and tryptic digestion may be simply
represented by the following schema, without any reference to the
^ " Lelirbuch der physiologisclien Cliemie," Jena, 1893, Tli. 1, S. 200.
VOL. I.- — 27



4i8 CHEMISTRY OF THE DIGESTIVE PROCESSES.

cleavage or any other theory, save in the names of such of the substances
as have been named on a theoretical basis : —

Peptic Digestiojs\ Trxptic Digestion.

Proteid. Protcid.

Acid Albumin Alkali Albumin

I I Deuteroalbumose

Protoalbuniose Heteroalbumose |

Antipeptone, amido-acids, etc.



Deuteroalbumose

I
Amphopeptone.

In the above account of the intermediate products formed between
proteid and peptone, an attempt has been made to point out how far
each important experimental result is in agreement with, or lends support
to, the cleavage theory of proteid digestion. Most of the results have
been obtained by supporters of that theory, but these results fall far
short of proving the truth of the theory, and may be explained without
reference to anti- and hemi-bodies. The main points may here be
summarised : —

1. Certain substances have been obtained by the action of dilute acids on
proteids, which do not yield amido-acids when subjected to prolonged tryptic
digestion ; these substances have been on this account looked upon as pure
anti-compounds. But there is no evidence that such substances are formed
naturally in either peptic or tryptic digestion : there is evidence against it in
the extreme difficulty with which they are attacked either by pepsin or
trypsin. J^either are these substances in their chemical behaviour albumoses,
so that the term antialbumose, as applied to any of them, is a misnomer.

2. The substance originally obtained from a fractionated peptic digestion,
and named hemialbumose, was afterwards shown by its discoverers to be a
mixture of three bodies, — protoalbumose, heteroalbumose, and deuteroalbumose,
— and none of these three discrete bodies was foiuid to be either a pure hemi-
albumose or pure antialbumose, so that, if the cleavage theory is to be main-
tained, we must be content to believe that each of these three is a mixture
in varying proportions of anti- and hemi-groups, and admit the existence of
antiprotoalbumose and hemiprotoalbumose, of antiheteroalbumose and hemi-
heteroalbumose, of antideuteroalbumose and hemideuteroalbumose, without
any experimental evidence whatever. Again, the cleavage theory takes no
account of the fact that loroto- and /ie^e?'oalbumose are formed prior to the
deuteroalbumose.

3. Amphopeptone is supposed to be a mixture in about equal proportions
of antipeptone and hemipeptone ; but these two bodies have never been isolated
from it. Antipeptone can only be obtained from amphopeptone by the action
of trypsin, and hemipeptone has never been obtained at all.

4. There is no doubt that some forms of proteids, or altered proteids, are
more easily decomposed by trypsin, yielding amido-acids, than are others ; but
this does not prove that such bodies are variable mixtures of a fraction which
is not decomposable at all with one which is completely decomposable. When
from an ampho-body there have been isolated two fractions, one a pure anti-
body that is completely unalterable by trypsin, the other a pure hemi-body
that is completely decomposable into amido-acids by trypsin, then it will be
time to believe in ampho-, anti-, and hemi-bodies. At present neither from
amphopeptone, protoalbumose, heteroalbumose, or deuteroalbumose has there



CLE A VA GE THE OR Y OF FRO TEID DIGESTION. 4 1 9

been such a separation, even iDartially, achieved, although these are admitted
to be ampho-bodies by the supporters of the theory.

But if the cleavage theory be not accepted, what explanation is there
for the fact that different albumoses yield varying accounts of amido-
acids, which suffer varying amounts of decomposition, under the action
of trypsin ?

The different proteids, and the products derived from them, differ so
little in chemical composition (and this is especially true for the various
albumoses), that the difference in their nature is probably due to a differ-
ence in atomic grouping. Is it not probable, then, that some of these
groups are much more susceptible of decomposition than others ; that
those albumoses which yield much amido-acid contain more groups in
their molecules which are decomposable by trypsin ; that those which
yield much antipeptone- contain less of these decomposable groups ; and
that in all cases that substance (or substances) which we call antipeptone
is the remainder after all those groups which are attackable by trypsin
have been removed in the form of amido-acids ?

It will be seen that this substitutes, for two molecules, one easily
attackable, the other wholly unattackable by trypsin, one molecule ; of
which a portion, variable in the case of each albumose, is attacked by the
trypsin and a residue left, in which there are no groups that the trypsin
is able to attack ; such a substitution relieves one from belief in a large
number of substances of which the existence has never been proven.

Again, if a cleavage of the proteid molecule takes place, at the begin-
ning of the digestive process, into anti- and hemi-groups, of which the
anti-groups, after passing through the albumose stage, become finally
converted into antipeptone, while the hemi-groups, after passing through
both albumose and peptone stage, become finally converted into amido-
acids, one would expect, in an interrupted tryptic digestion, to find
these intermediate hemi-products mixed with the intermediate anti-
products ; to find substances, corresponding to those found in peptic
digestion, which w^ould become on more complete tryptic digestion
partially, at least, broken up into amido-acids. No such compounds or
mixtures are, however, actually found ; no hemi-compound is ever found
at any stage of tryptic digestion. As already stated, 'proto- and hetero-
albumose are never formed, only deuteroalbumose.

Neither is there any evidence of the formation of such a substance
as amphopeptone in tryptic digestion, only antipeptone is formed. In
short, there is no evidence whatever in tryptic digestion of two parallel
series of anti- and hemi-bodies proceeding pari passu into anti- and hemi-
peptones, of which the latter becomes decomposed into amido-acids. If
any hemi-bodies are formed, they are at once broken down into amido-



Online LibraryE. A. (Edward Albert) Sharpey-SchäferText-book of physiology; (Volume v.1) → online text (page 59 of 147)