QUALITATIVE CATABOLIC REACTIONS OF BACTERIA 71 
V. QUALITATIVE CATABOLIC REACTIONS OF BACTERIA. 
The chemical changes observed in cultures of ordinary bacteria are 
chiefly those associated with the breakdown of organic substances for 
energy— they are reactions of the catabolic phase of bacterial metab- 
olism. It should be again emphasized that the energy reactions— the 
catabolic reactions— are those which are most profoundly influenced 
by the composition of the nutritive substrate upon which the organisms 
are grown. 
A. Reactions of Bacteria in Media Containing Only Nitrogenous 
Substances (Proteins or Protein Derivatives) Which are Utilized for 
the Energy Requirements of Bacteria. — Proteins are composed of 
amino-acids, of which some seventeen are recognized. Bacteria which 
decompose protein appear to act upon these amino-acids in the last 
analysis, and several types of reaction are recognized at the present 
time. Each kind of organism utilizes protein or protein derivatives 
somewhat differently and characteristically, but in general one or more 
of the following types of reactions are involved either successively or 
simultaneously in the catabolism of these substances. The reactions 
follow •} 
1. R.CH0.CHNH2.COOH + H2 - R.CH2.CH2.COOH.+ NH3. 
Reductive deamination of amino-acid to fatty acid with the same 
number of carbon atoms. 
2. R.CH2.CHNH2.COOH + H2O = R.CH2.CHOH.COOH + NH3. 
Hydrolytic deamination of amino-acid to oxy-acid with the same 
number of carbon atoms. Lactic acid may be produced from alanin 
bv this reaction. 
'.3. R.CH2.CHNH2.COOH + O = R.CH2.CO.COOH + NH3. 
Deamination and simultaneous formation of an alpha ketonic acid. 
(Pyruvic transformation.) Neuberg- has shown that pyruvic acid and 
other alpha keto acids are rapidly changed to aldehydes having one less 
carbon atom, with the simultaneous liberation of CO2 bv the action of 
the enzvme carboxvlase, thus: CH3.CO.COOH -^ CHJ.CHO + CO 2. 
4. R.CH2.CHNH2.COOH -. R.CH0.CH2.XH2 + CO2. Carboxylic 
decomposition of amino-acid to amine with one less carbon atom. 
5. R.CH2.COOH -> R.CH2.CH3. + CO2. Carboxylic decomposi- 
tion of fattv acid. 
6. R.CH2.CH0.COOH + 30 = R.CH2.COOH + CO2 + H2O. 
Carboxylic decomposition with the formation of a fatty acid with one 
less carbon atom. 
A few illustrations will indicate the nature of these changes in amino- 
acids with the production of certain substances of clinical interest: 
1. Formation of indol from tryptophan. Indol is a substance pro- 
duced in the intestinal tract from tryptophan (an amino-acid found 
in protein), chiefly by B. coli and B. proteus. The reactions through 
1 See Kruse: Allgem. Mikrobiol., pp. 505-536, for literature. 
2 See Neuberg: Handb. d. biol. Arbeismeth., 1927, abt. iv, 1, 565. 
