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Amine metabolism in mycobacteria isolated from poikilothermic animals. Evelyn, Trevor Patrick Todd

Abstract

Three mycobacterial strains isolated from fish were tested for their ability to metabolize various amines, supplied individually as sources of carbon. A series of six aliphatic and two cyclic amines was used. Growth occurred only in putreseine. The ability to oxidize putrescine was enhanced by growing the cells in the presence of this compound. One mycobacterial strain appeared to possess some ability to oxidize putrescine without pre-exposure to the compound. However, when cells of this strain were examined for the presence of putrescine and related polyamines, no such compounds were detected. In the mycobacterial strains tested, putrescine did not appear to affect the rate of endogenous respiration. Therefore, in reporting oxygen consumption due to putrescine, the endogenous oxygen consumption has been subtracted from the total oxygen uptake. During the oxidation of putrescine, the oxygen uptake curves "broke" at a point corresponding to approximately 43% of the maximum level of oxidation. Thereafter, very small increases in the level of oxidation occurred, so that by the end of the experiment, over 50% of the molecule appeared to be assimilated. Up to 69-76% of the amino-nitrogen of the putrescine molecule was released as ammonia during the reaction, the rest of the nitrogen being assimilated. Measurement of carbon dioxide production using 1,4-C¹⁴ putrescine revealed that under CO₂-free conditions, at least 1.5 μM of carbon dioxide were released per μM of putrescine. When cells were incubated with 1,4-C¹⁴ putrescine, 25% of the radioactivity was assimilated. The remaining radioactivity was liberated as C¹⁴O₂. Chemical fractionation of the cells indicated that fractions containing lipid, nucleic acid and protein were labelled. Cell-free extracts obtained from putrescine-adapted cells contained four enzymes responsible for the conversion of putrescine to succinic acid. The enzymes occurred in the 10,000 X G supernatants of the cell-free extracts and were all active at pH 9.0. Putrescine was oxidatively deaminated to yield Δ' -pyrroline. The latter compound was then oxidized to ɣ-aminobutyric acid by a dehydrogenase enzyme requiring NAD or NADP. Gamma-aminobutyric acid underwent a transamination with α-ketoglutaric acid to yield succinic semialdehyde and glutamic acid. Succinic semialdehyde was oxidized to succinic acid by an NAD- or NADP- requiring dehydrogenase. The specificity for putrescine, shown by the tested mycobacterial strains, is discussed.

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