Variations in the pathways of malate oxidation and phosphorylation in different species of Mycobacteria

Mycobacterium tuberculosis H₃₇ Rv, the slow-growing human pathogenic strain of tubercle bacilli and Mycobacterium smegmatis and Mycobacterium phlei, the fast-growing saprophytes, have shown variations regarding the type of dehydrogenase that initiates malate oxidation in the respiratory chain.M. tuberculosis H₃₇Rv is characterized by having a malate oxidase system (designated MAL_NAD pathway) in which malate oxidation is mediated by the NAD⁺_? dependent malate dehydrogenase (EC 1.1.1.37) but not by FAD-dependent malatevitamin K reductase. M. smegmatis possesses a different malate oxidase system (designated MAL_FAD pathway) in which malate oxidation is exclusively carried out by the FAD-dependent malate-vitamin K reductase because NAD⁺-dependent malate dehydrogenase is absent in this organism. M. phlei has a mixed system of malate oxidase (designated MAL_NAD+FAD pathways) in which both the NAD⁺_? and FAD-dependent dehydrogenases take part. In all the three systems, the rest of the electron transport chain is common.