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Factors Affecting the Activity and Synthesis of NAD-dependent Lactate Dehydrogenase in Rhizopus oryzae
Abstract
Summary: The NAD-dependent lactate dehydrogenase of Rhizopus oryzae, like some bacterial lactate dehydrogenases, catalyses reduction of pyruvate by NADH but not the reverse reaction. It will, however, catalyse reduction of the NAD+ analogue, 3-acetylpyridine adenine dinucleotide (APAD+) by l(+)-lactate; NAD+ does not inhibit the rate of APAD+ reduction in this reaction. The relationship between pyruvate reductase activity and NADH concentration is sigmoidal with a high apparent K m for NADH (2·9 × 10−4 M).
Enzyme level reaches a peak during early vegetative growth of the mycelium and declines rapidly before sporulation. The peak level reached is dependent on the glucose concentration of the medium, being greatest in high glucose media. When grown in media containing growth-limiting concentrations of glucose, lactate dehydrogenase activity is negligible. Transfer of such mycelia to high glucose media results in a rapid increase in the specific activity of the enzyme; this increase is prevented by cycloheximide. High levels of lactate dehydrogenase can also be induced by growing the fungus in media containing growth-limiting concentrations of zinc.
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© Society for General Microbiology, 1973