Regulation of lactate/pyruvate ratios by cyclic AMP in Neurospora crassa.

Cyclic AMP is thought to have a general role in stimulating the breakdown of carbohydrate reserves and subsequent glycolytic activity. This would be expected to increase the availability of reducing equivalents in the form of cytoplasmic NADH. The current study examines another potential reaction controlling cytoplasmic NADH in the fungus Neurospora crassa, that of lactate dehydrogenase, to determine whether it is also regulated by cyclic AMP. The cr-1, adenylate cyclase and cyclic AMP-deficient mutant, grown with and without exogenous cyclic AMP was compared with an isogenic wild type. The results show that cyclic AMP raises pyruvic acid pools and lowers both lactic acid pools and lactate/pyruvate ratios. It does that, in part or in whole, by lowering lactate dehydrogenase activity. The possibility that cytoplasmic NAD+/NADH is a major target of cyclic AMP control is discussed. The high performance liquid chromatography procedures used in these studies are applicable to the measurement of intracellular pools of tricarboxylic acid cycle and other organic acids.