Studies on Pyruvate Metabolism and Cytochrome System in Neurospora Tetrasperma

Abstract

Attempts to demonstrate the oxidation of pyruvate by cell-free extracts of ascospores and mycelium of N. tetrasperma by any of the commonly used methods of extraction and mixtures of co-factors were unsuccessful. Adding a dye, p-phenylenediamine (PPD) did stimulate O2 uptake when pyruvate was added to extracts of dormant and activated ascospores, conidia, and mycelia. Further experiments showed that this O2 uptake is probably due not to oxidation of pyruvate but to oxidation of the decarboxylation product of pyruvate, acetalde-hyde, formed from pyruvate by the carboxylase in these extracts. Acetaldehyde was oxidized by these extracts enzymatically but only in the presence of PPD. O2 uptake by mycelial extracts in the presence of PPD alone has been shown to be due to the oxidation of endogenous cytochrome c by cytochrome oxidase. The endogenous cytochrome c content was measured spectroscopically. Lack of O2 uptake by extracts of dormant ascospores in the presence of PPD suggests a low level of endogenous cytochrome c in these extracts. On the other hand, the level of cytochrome oxidase is higher in the dormant ascospore extracts than in the mycelial extracts. The low level of cytochrome c may in part account for the low rate of respiration in the dormant ascospores.