The kinetics of the oxidation of benzoic acid by certain Mycobacteria.

Benzoic acid is oxidized by certain Mycobacteria (1). They do not oxidize it completely to carbon dioxide and water; the oxygen uptake usually stops when 5 atoms of oxygen are utilized for each molecule of benzoic acid. The enzymes concerned are adaptive, and are rapidly formed when small amounts of benzoic acid are added to suspensions of the bacteria (2). Benzoic acid may be considered somewhat toxic to the bacteria, because, although small amounts stimulate enzyme formation, larger amounts slow down or inhibit the process, possibly by interfering with reactions providing the energy for the enzyme synthesis. Furthermore, as shown below, the enzyme once formed disappears fairly rapidly in the absence of benzoic acid. Streptomycin prevents the formation of these adaptive enzymes, and thus inhibits oxidation of benzoic acid (2). The rate of oxygen uptake has been carefully measured and the following is an analysis of the kinetics of the reactions involved. Data were obtained from experiments done with Mycobacterium tuberculosis BCG 8240. The technique has already been described (1, 2). Oxidation of benzoic acid by Mycobacteria proceeds by a number of stages. The substances formed, for the most part, have not been isolated, and will be referred to by letters. Benzoic acid (A) is first hydrated (cf. (3)) to form B. B takes up 1 atom of oxygen and becomes C. C, in turn, takes up a second atom of oxygen to become D, and so on through E, F, and G, until 5 atoms of oxygen have been taken up for each molecule of the original benzoic acid. The time course of each of these reactions, since there is no change in the concentrations of either water OF oxygen, will probably be monomolecular. Using small letters to mean “concentration of,” we may express these rates as follows: