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Charles E. (Charles Edmund) Simon.

A text-book of physiological chemistry : for students of medicine and physicians online

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tvrosin, it likewise results on artificial decomposition of the albu-
mins Avith dilute mineral acids and alkalies, and is also formed
during the process of albuminous putrefaction. Outside the in-
testinal canal asparaginic acid has not been found in the animal
body. In the form of its amide asparagin, however, it is widely
distributed in the vegetable world, and supposedly plays an im-
portant role in the synthesis of the vegetable albumins.

The substance crystallizes in rhombic prisms, which are soluble
with difficulty in cold water, but are quite soluble in hot water. In
absolute alcohol it is insoluble. Its aqueous solutions are laevorota-
tory, while in the presence of nitric acid dextrorotation is observed.

As has been shown (page 88), asparaginic acid is a dibasic acid



THE END-PRODUCTS OF ALBUMINOUS DIGESTION. 209

of the fatty series. It is amido-suceinic acid, and is represented by
the formula CH,.CI-I(NHo).(COOH),. It can be obtained from
asparagin on boiling with hydrochloric acid, as shown in the
equation :

CH2.CONH2 CH2.COOH

I + HjO = I -I- NHo.

CH(NH2).C00H CH(NH,).COOH

Asparagin. Asparaginic acid.

It has also been produced synthetically. On reduction it yields
succinic acid, as has been shown.

With cupric oxide asparaginic acid forms a crystalline compound
which is almost insoluble in cold water, but dissolves in boiling
water with comparative ease. This property is utilized for the pur-
pose of isolating the substance from the mixture of digestive
products.

Glutaminic Acid. — Whether or not glutaminic acid is formed
during the tryptic digestion of the albumins in general has not as
yet been ascertained. Kutscher claims to have found it in the
so-called antipeptone of Kiihne, which was obtained from fibrin.
On boiling with strong mineral acids, however, it is constantly
formed. But it is noteworthy that much larger quantities are found
if the decomposition of the albumins is eifected with hydrochloric
acid than with sulphuric acid. Kutscher thus found only 1.8 per
cent, among the decomposition-products of casein when using sul-
phuric acid, while Hlasiwez and Habermann obtained as much as
29 per cent, when hydrochloric acid was used. This is, of course,
remarkable, and it would be exceedingly interesting to ascertain the
fate of those radicles which can yield so large an amount of gluta-
minic acid when decomposition is effected by hydrochloric acid.

Glutaminic acid crystallizes in small glistening crystals, which
are soluble with difficulty in cold water, while in boiling water they
dissolve with greater ease, but separate out on cooling. With acids
and alkalies it combines to form salt-like products, among which the
hydrochlorate is conveniently utilized for the purpose of identifying
the substance. The melting-point of this compound is 193° C

The composition of glutaminic acid is expressed by the formula
CH..CH,.CH(NH,).(COOH),. It is thus amido-glutaric acid, and
bears the same relation to glutamin as that which exists between
asparaginic acid and asparagin. This is represented in the equation :

/CONH2 /COOH

CH2.CH2.CH(NH,)< + HP = CH^.CH^.CHfNH,)/ + NHo^

\COOH \COOH

Glutamin. Glutaminic acid.

On reduction it yields glutaric acid.

Isolation of Asparaginic Acid and Glutaminic Acid. — To isolate the
two acids in question among the products of tryptic digestion, the
mixture must first be freed from albumins and albumoses, as has
been described. The remaining solution is acidified with sulphuric

14



2i0 THE PRODUCTS OF ALBUMINOUS DIGESTION.

acid and precijiitated with phosphotungstic acid. The filtrate is
freed from sulphuric acid and any excess of the phosphotuno-stic
acid by means of barium hydrate. From the resultinoc filtrate
leucin and tyrosin are then removed by concentration. The mother-
liquor contains the glutaminic acid and asparaginic acid. These
are now separated from each other in the following manner : the
diluted solution is brought to the boiling-point and digested with
carbonate of copper. It is filtered while still hot, and precipitated
with subacetate of lead, care being taken to avoid an excess. This
precipitate is decomposed with hydrogen sulphide, and the filtrate
concentrated to a small volume. On standing, a crystalline mass is
obtained, which is then dissolved in boiling water and digested wnth
an excess of carbonate of copper, as before. The hot filtrate is
again concentrated, when on standing the copper salt of asparaginic
acid separates out in characteristic groups of needles. The filtrate
is freed from copper by means of hydrogen sulphide, concentrated^
and set aside, wdien the glutaminic acid crystallizes out.

GlycocoU. — AVhile it is generally known that glycocoll plays an
important part in the nitrogenous metabolism of the animal body^
and is intimately concerned in the formation of urea, hippuric acid,
phenaceturic acid, certain biliary acids, and in birds and reptiles of
uric acid, it is of interest to note that the substance has thus far
not been found as such among the products of pancreatic digestion,
although its radicle is manifestly present in certain albumoses. On
hydrolvtic decomposition with mineral acids, on the other hand,
giycocoU can be obtained from most albumins, but is especially
abundant in collagen, viz., gelatin. Two exceptions to this general
rule, however, are noted, viz., casein^ and (according to Magnus-
Levy) the peculiar albuminous substance which is known as the
Bence Jones' body, and from either of these it is also impossible to
obtain a hetero-albumose. The hetero-albumose of fibrin, according^
to Spiro, yields a considerable amount of glycocoll, while from the
proto-albumose it cannot be obtained.

Heretofore the isolation of glycocoll and its recognition as such
were attended with great difficulties. A somewhat simpler pro-
cedure, however, has recently been suggested by Baum, and with
its aid Spiro was able to show that, contrary to former views, the
substance can be obtained not only from the albuminoids, but also
from the native albumins, with the exceptions indicated. The
method is based upon the observation that glycocoll can be trans-
formed into hippuric acid in the test-tube by treating with benzoyl
chloride in the presence of sodium hydrate, and that the formation
of the resulting hippuric acid can be readily demonstrated by con-
densing this with benzaldehyde in the presence of sodium acetate
and acetic anhydride. The lactimide of benzoyl-amido-cinnamic
acid is thus formed. On decomposition with sodium hydrate this
yields phenyl-pyro-racemic acid, which in ethereal solution gives a

» K, Fischer states that casein contains traces of glycocoll.



THE END-PRODUCTS OF ALBUMINOUS DIGESTION. 211

green color on treating with chloride of iron. With phenyl-
hydrazin, moreover, it forms an osazon which melts at 161° C.
These changes may be represented by the equations :

(1) CH2.(NH2).COOH + CeHs.COCl = CHj.NH(C6H5.CO).COOH + HCl
GlycocoU. Benzoyl chloride. Hippuric acid.

C2) CH2.NH(CfiH5.CO).COOH + CgHsCOH = CgHs.CO.N.CrCH.CeHj + 2H,0

Hippuric acid. Benzaldehyde. I /

CO

Lactimide.

(3) CeHa.CO.N.CiCH.CeHs CeHj.CONH^— C— COOH

1/ + H,0 = , II

CO CH-CgHs

Lactimide. Benzyol-amido-cinnamic acid.

(4) CeHs.CONH^— C— COOH

II + H2O = CfiHgCO.NH^ + CgHs.CHj-CO.COOH
CH. CgH- Benzamide. Phenyl-pyro-racemic

Benzyol-amido-cinnamic acid.

acid. ■(

Method. — The decomposition of the albumins (gelatin) is effected
by prolonged boiling with dilute sulphuric acid — 25 per cent, solution.
The excess of acid is removed with plumbic carbonate. The filtrate
is concentrated, freed from any tyrosin that may have separated out,
and then benzoylated with benzoyl chloride in the presence of
sodium hydrate. Care should be had that the reaction of the solu-
tion is constantly alkaline during this process. The hippuric acid
is then extracted with acetic ether. The dried substance is now
treated with tliree molecules of acetic anhydride, one molecule of
sodium acetate, and one molecule of benzaldehyde. The mixture is
heated on a water-bath for half an hour. The condensation-produce
is then treated with water and gently warmed. The oil that sepa-
rates out is dissolved in hot alcohol and allowed to cool. The lacti-
mide then crystallizes out, and can be recognized as follows: the
substance is heated with a strong solution of sodium hydrate
until a distinct odor of ammonia is noticed. This is due to
the decomposition of the benzamide. On acidifying the solution
the phenyl-pyro-racemic acid separates out and can be readily ex-
tracted by shaking with ether. One portion of the ethereal extract
is treated with a dilute solution of the sesquichloride of iron, when
on agitation the watery layer assumes a dark-green color, which
gradually changes to a characteristic yellow. The other portion is
treated with an ethereal solution of phenylhydrazin, which leads to the
separation of the hydrazon of phenyl-pyro-racemic acid. After wash-
ing with ether this may be identified by its melting-point — 161° C.

As regards the general properties of glycocoll and its preparation
as such, see pages 87 and 278).

Tryptophan. — Tliis substance is apparently always formed when
the tryptic digestion of the albumins has extended beyond the forma-
tion of albumoses. As its presence among the various digestive
products is easily recognized, it is thus possible to ascertain whether



212 THE PRODUCTS OF ALBUMINOUS DIGESTION.

the destruction of the albuminous molecule has extended to the
formation of amido-acids, Avithout testing; for these directly. Like
the amido-acids, it is also formed during the hydrolytic decomposi-
tion of the albumins with baryta-water, and likcM'ise results during
the process of intestinal pntrefaction. Of special interest is the fact
that while the primary albumoses of fibrin, as also the secondary
albumose-A, on further digestion with tr^^psin, give rise to the
formation of tryptophan, the secondary albumose-B apparently does
not contain the chromogenic group.

Hopkins and Cole have shown that tryptophan is skatol amido-
acetic acid :

/C(CH3)^
CbHZ '>C.CH(NH2).C00H
\I?H'

To the presence of this complex in the albuminous molecule the
reaction of Adamkiewicz is due (see page 38).

With chlorine and bromine it yields at least three colored products,
the so-called proteinochromes. Of the bromine products, one is a
bluish-violet substance, and contains about 35 per cent, of bromine ;
the second is a red body, with 27 per cent. ; and the third a brovrn
pigment, with the same amount of bromine.

According to Xencki, a certain similarity exists in the percentage
composition of the red pigment with hsematoporphyrin, viz., l)iHru-
bin, and of the brown pigment with the so-called melanins. Tryp-
tophan, moreover, like hsematin and hsematoporphyrin, yields pyrrol,
hydrogen sulphide, methyl mercaptan, indol, and skatol on fusion
with caustic alkali.

Test. — The test for tryptophan and the isolation of the three
known pigments is conducted as follows : the digestive mixture
is acidified with acetic acid and treated with two and one-half times
its volume of saturated bromine-water. A beautiful reddish-violet
precipitate is thus formed, which increases on standing. After
twentv-four hours this is filtered off. On the further addition of
bromine-water the brown pigment separates out on standing. The
red pigment will be found in the violet precipitate, and can be iso-
lated as follows : the precipitate is first washed with water and then
extracted with dilute ammonia ; this extract is precipitated with
acetic acid. The precipitate is separated from the brown filtrate,
redissolved in very dilute ammonia, again precipitated with acetic
acid, and washed with water. It is then extracted with amyl
alcohol ; this dissolves the red bodv. The alcohol is evaporated
off at 40° C, the residue dried at 106° C, and finally washed with
ether. The violet pigment is obtained on further extraction of the
violet precipitate with a little stronger solution of ammonia than in
the first instance. The substance is precipitated with acetic acid,
well washed with water, and extracted with 95 per cent, alcohol.
The alcoholic extract is evaporated to dryness at 40° C, the residue
dried at 106° C. and washed with petroleum ether.



THE END-PRODUCTS OF ALBUMINOUS DIGESTION. 213

To isolate the brown pigment, finally, the second bromine pre-
cipitate is filtered off, washed with water, dissolved in very dilute
ammonia, reprecipitated with acetic acid and washed with Avater,
and briefly with 95 per cent, alcohol, both of which dissolve a por-
tion of the pigment. It is then dried and washed with ether. The
resulting product is almost black.



CHAPTER X.

BACTEEIAL ACTION IN THE INTESTINAL TRACT.

I HAVE pointed out in a preceding chapter that the gastric juice
possesses marked germicidal and antiseptic properties, so that a large
number of bacteria which are constantly swallowed with the saliva
and the food are subsequently destroyed in the stomach. A perfect
barrier to the invasion of micro-organisms, however, does not exist,
and after having passed the pylorus they are placed in surround-
ings which are in all respects most favorable to their develop-
ment. Here they take an active part in the decomposition of the
various food-stuffs which have escaped digestion in the stomach, and
further modify the digestive products which have already been
formed, as also those which result from the action of the various
intestinal ferments. The greater portion of the products of normal
digestion, however, escapes the specific activity of the bacteria, and
is absorbed in a form which can be utilized by the body for purposes
of nutrition. Formerly it was supposed that the biliary acids played
an important part in preventing undue activity on the part of the
bacteria, but this view has now been largely abandoned, and we are
totally ignorant as to the manner in which the body here protects
itself against excessive bacterial action. It has been argued that an
accumulation of the decomposition-products which result from the
action of bacteria upon the various food-stuffs in itself inhibits the
further activity of the organisms, but Ave can hardly regard such an
explanation as valid in view of the fact that in the intestiues these
decomposition-products are to a large extent absorbed, and it seems
more probable that a vital activity of the epithelial cells is here
of prime importance. In the small intestine at least, where peri-
stalsis is extremely active, and where the intestinal contents are
churned in such a manner that the individual particles are almost
constantly in contact with the intestinal walls, we accordingly find
that bacterial action is not nearly so extensive as in the large intes-
tine, where the opposite conditions prevail. In the clinical labo-
ratory we find, as a matter of fact, that the degree of intestinal
putrefaction increases at once when the peristalsis of the small
intestine is impeded, and reaches its greatest height if the secretion
of hydrochloric acid becomes arrested at the same time.

In former years a tendency existed among physiologists to regard
bacterial action in the intestine as serving a useful ]iurposc, and it
was even supposed that, as in the case of plants, animal life could
not go on in the absence of micro-organisms from the alimentary

214



BACTERIAL ACTION IN THE INTESTINAL TRACT 215

canal. This view has now been abandoned, however, especially
since Thierfelder and Nuttall were able to demonstrate that guinea-
pigs, after removal from the uterus of the mother by Csesarean
section, can be maintained in perfect condition as to health and
body-weight when fed on sterile food and when furnished with
sterile air exclusively. On subsequent examination it was shown
that the intestinal contents of these animals were also sterile. We
may thus conclude that the presence of bacteria in the intestinal
contents is at best unnecessary, and it is doubtful, indeed, whether
they serve a useful purpose at any time.

The action of bacteria upon the food-stuifs is in certain respects
quite analogous to that of the digestive ferments which are fur-
nished by the digestive glands of the animal body. The primary
digestion of the original material, however, does not cease with the
production of substances which the animal can subsequently utilize
for the purpose of replacing tissue, but is, on the whole, far more
extensive. Polysaccharides and disaccharides are thus not only
inverted to monosaccharides, but the latter are subsequently further
decomposed into material in which but little potential energy, if
any, remains stored. Albumins are similarly decomposed, with
the ultimate formation of substances which in part at least are dis-
tinctly toxic ; and the fats are divided into their components, which
are then further broken down, with the final formation of fatty
acids of the lowest order, etc. A great variety of decomposition-
products thus result from the normal food-stuffs, which are further
increased by those arising from material which the ferments of
the animal itself are incapable of digesting. To these are added
the decomposition-products of the various biliary constituents and
of the albuminous secretions which are poured into the intestinal
canal by the digestive glands themselves.

As has been pointed out, the most intense degree of bacterial
action is observed in the large intestine, and it is interesting to
note that while albuminous putrefaction here prevails, the fermenta-
tive processes in the more restricted sense of the term, viz., the
decomposition of carbohydrates and fats, occur almost exclusively in
the small intestine. This difference may be dependent to a certain
degree upon the difference in the reaction of the intestinal contents
in the two sections of the gut — that of the small intestine in its lower
portion at least being acid, while the reaction of the contents of the
large intestine is usually alkaline. But it is also possible that other
and still unknown factors determine this difference, and that the
varying reaction is primarily due to the decomposition-products
directly which result from the action of the bacteria. Among these
factors the relative amount of water may be of importance.

Nencki, MacFadyen, and Sieber, who had occasion to study the
chemical composition of the intestinal contents in a patient in whom
an artificial anus had been established at the distal end of the ileum,
give the following account of their observations : The reaction was



216 BACTERIAL ACTION IN THE INTESTINAL TRACT.

quite constantly acid, owing to the presence of organic acids, and
notably of acetic acid. Other acids that were present were lactic
acid, paralactic acid, various volatile fatty acids, succinic acid, and
the biliary acids. The odor but rarely suggested the existence of
putrefactive changes. Indol, skatol, and phenol could not be
demonstrated as such, although the urine contained indiean on
several occasions. Leucin and tyrosin were not found. Alcohol
could always be demonstrated. Of gases, carbon dioxide Avas ob-
served, as also faint traces of hydrogen sulphide, while methyl-
mercaptan was absent.

Carbohydrate fermentation thus manifestly stands in the fore-
ground, and is exemplified in various types by the equations :

(1) CgHjjOg = 2C2H5.OH + 2CO2, alcoholic fermentation.

(2) C2H5.OH + 20 = CH3.COOH 4- H2O, acetic acid fermentation.

(3) C6H,206 = 2CH3.CH(OH)COOH, lactic acid fermentation.

(4) 2C3H6O3 = C3H..COOH + 2CO2 + 4H, butyric acid fermentation.

The products of albuminous putrefaction, on the other hand, are
almost exclusively formed in the large intestine. Primarily they
are in part at least the same as those which result from the action
of trypsin on albumins, and in experiments in vitro we thus find
albumoses, peptone-like bodies, tryptophan, leucin, tyrosin, aspara-
ginic acid, and glutaminic acid. In the contents of the large intes-
tine, however, these substances are found only in traces, so that we
are forced to the conclusion that they are either absorbed as soon as
formed or that they are further decomposed. Both, no doubt,
occurs, and related bodies are, as a matter of fact, encountered in
the feces. As a result of bacterial activity still other substances
are formed, however, which are apparently not derived from the
final products of digestion, but which are formed from the more or
less intact albuminous molecule directly.

The more important decomposition-products which result from
the action of bacteria upon the products of albuminous digestion are
here considered.

Indol. — Indol is a derivative of the tryptophan complex, viz., of
skatol-amido-acetic acid :



NH'



CgH/ ^C.CH(NH2).C00H

\-« — —



Structurally it is closely related to indigo, and according to
Nencki this transformation can be effected through the action of
ozone. It is represented by the equation :

/CH ^ / CO V / CO .

2C6H / >CH + 40 = CeH / >C = C( ^CeH, + 2H2O.

Indol. Indigo.

Conversely, indigo can be transformed into indol on reduction.



SKATOL. 217

From the albumins the substance can also be obtained on fusion
with potassium hydroxide (see page 42).

The greater portion of the indol that is formed in the large in-
testine is no doubt eliminated in the feces. A certain amount,
however, is absorbed, and after oxidation to indoxyl appears in the
urine in combination with sulpiiuric acid as so-called indican
(pages 90 and 269). If larger quantities are formed, a variable
fraction is further eliminated in the urine as an indoxyl compound
of glucuronic acid.

Indol crystallizes in small platelets, which melt at 52° C, and
are soluble in hot water, ether, alcohol, and benzol. Its odor is
feculent ; it is quite volatile, and when boiled Avith water passes over
into the distillate. With picric acid it forms a beautifully red crys-
talline compound, which is readily decomposed, however, on boil-
ing with dilute ammonia, and the liberated indol is then found in
the distillate. On distilling in the presence of sodium hydrate, on
the other hand, the indol is decomposed.

Tests. — When treated in aqueous solution with nitric acid and a
trace of sodium nitrite a red precipitate of the nitrate of nitroso-
indol is formed. This is soluble in alcohol and crystallizes out upon
the addition of ether.

If a small piece of pine wood is moistened with strong hydro-
chloric acid and then placed in a watery solution of indol, it gradu-
ally assumes a cherry-red color.

An aqueous solution of indol is treated with a small amount of
a solution of sodium nitroprusside until a brownish-yellow color
develops. If now a dilute solution of sodium hydrate is added
drop by drop, the color changes to violet. Upon the further addi-
tion of a little dilute hydrochloric acid this becomes a deep blue,
while an excess of the acid destroys the blue color.

For the isolation of indol, see page 224).

Skatol. — Skatol, like indol, is a direct derivative of tryptophan,
and is likewise formed during the process of albuminous putrefac-
tion. It is a methylated indol, and may be represented by the
formula :

yC(CH3)^

By combining with carbon dioxide it gives rise to the formation
of skatol-carbonic acid, which is also found in the contents of the
large intestine, and belongs to the ortho-series. Its formula is

CfiHZ "^C.COOH.

Like indol, skatol is also formed on fusing albumins with caustic
soda, and can be obtained from indigo on reduction with tin and
hydrochloric acid. When passed through a red-hot tube it yields



218 BACTERIAL ACTION IN THE INTESTINAL TRACT.

indol. On absorption, it is oxidized to skatoxyl and is eliminated
in the urine in combination Avith sulphuric acid and glucuronic
acid, as in the case of indol (see pages 90 and 272). Skatol-car-
bonic acid, on the other hand, appears in the urine as such.
Another derivative of skatol is Bauni's skatosin — CioH„3X,02.

Skatol crystallizes in fine platelets, which melt at 95° C. aiid are
readily soluble in ether, alcohol, and benzol ; in hot water it is
soluble with greater difficulty than indol. Its odor is exceedingly
oiiensive. Like indol, it is volatile, and combines with picric acid
to form a red crystalline compound. On distilling this in ammo-
niacal solution or in the presence of sodium hydrate the skatol passes
over as such, while indol in the latter instance is decomposed. On
distilling a mixture of indol and skatol in aqueous solution the



Online LibraryCharles E. (Charles Edmund) SimonA text-book of physiological chemistry : for students of medicine and physicians → online text (page 23 of 58)