http://www.europa.com/~rsc/cancer/pip.txt
Referrence 33, rcrs020197.txt

From the Classic: 

            Introduction to Physiological Chemistry
                             by
                Meyer Bodansky, Ph.D., M.D.
Director of Laboratories, John Sealy Hospital, Galveston, and Professor
         of Pathological Chemistry, University of Texas

                         Third Edition

                    John Wiley & Sons, Inc.
               London: CHAPMAN & HALL, LIMITED
                             1934. 

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[p.204, Par.1]

Products of Intestinal Putrefaction[22]

The contents of the large intestine undergo bacterial or putrefactive
changes.  Concerning bacterial action on fat, little can be said except
that it results in the formation of fatty acids and glycerol.  From
lecithin may be formed choline, neurine, muscarine, and related
compounds.

CH3   CH2---CH2OH   CH3   CH==CH2   CH3   CH2CHO
   \ /                 \ /             \ /
CH3-N               CH3-N           CH3-N
   / \                 / \             / \
CH3   OH            CH3   OH        CH3   OH
 Choline             Neurine          Muscarine

The carbohydrates yield a variety of substances, including oxalic acid,
the lower fatty acids[23] and their derivatives--formic, acetic,
propionic, lactic, butyric, oxybutyric, and succinic--acetone, and the
gases carbon dioxide, methane, and hydrogen.  If present in sufficient
amount, some of the products of carbohydrate fermentation may act as
irritants to the intestinal tract and cause diarrhea.

Bacterial enzymes acting on protein yield proteoses, peptones, amino
acids, ammonia, and hydrogen sulfide.  From the aromatic amino acids are
formed indole, skatole, phenol, cresol, and tyramine.  Cadaverine,
putrescine, and ethylidene-diamine are among the toxic amines, or
ptomaines, formed from amino acids in putrefaction.  Ethyl
mercaptan(C2H5SH), methyl mercaptan (CH3SH), and hydrogen sulfide owe
their origin to the putrefaction of cystine.

With regard to the formation of these substances, much remains to be
learned, but sufficient is known to enable us to consider briefly the
chemistry of some of the reactions involved.  Among the more important of
these is one involving the removal of a carboxyl group (decarboxylation),
presumably due to an enzyme, carboxylase, present in the bacteria.
Another reaction consists in the splitting off of an amino group by
deaminization.  Reduction, due to a reductase, and reactions of
hydrolysis as well as of oxidation are also believed to occur.

Referrences

22. For a comprehensive survey of the subject, the student is referred to
     Marjory  Stephenson's "Bacterial Metabolism," Longmans, Green & Co.,
     London, 1930.
     
23. Grove, Olmstead and Koenig, J.Biol. Chem., 85, 127 (1929-30).
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