EXOGENOUS NADH OXIDATION AND PARTICULATE FUMARATE REDUCTASE IN MYCOBACTERIUM PHLEI

Bacteria contain a number of distinct pathways that are capable of oxidizing NADH. Only one of the NAD+-linked pathways, that of the electron transport particles, has been shown to be linked to the generation of energy-rich phosphate bonds. Regulation of the phosphorylative pathway associated with the oxidation of NADH by the system from Mycobacterium phlei appears to be controlled by the level of NAD+, AMP, and inorganic phosphate. The phosphorylative and nonphosphorylative pathways were inhibited by NAD+; however, relief of inhibition of NADH oxidation by NAD+ was found to occur only with the phosphorylative pathway on addition of inorganic phosphate and AMP. Kinetic studies indicated that the inhibition by NAD+ on NADH oxidation by either pathway was allosteric in nature; however, AMP and inorganic phosphate alter only the kinetic pattern exhibited by the phosphorylative pathway. In addition, fumarate which is one of the chief carbon sources used to support the growth of M. phlei, was found to stimulate the cell-free phosphorylative pathway associated with NADH oxidation. Under these conditions fumarate was found to accept electrons from cytochrome b reduced by NADH and to form succinate. The oxidation of cytochrome b by fumarate and the formation of succinate from fumarate were inhibited by hydroxyquinoline-N-oxide. The fumarate reductase appeared to be localized in the electron transport particles and was cytochrome b-Iinked. © 1969.