ORGANIZATION AND REGULATION OF THE MITOCHONDRIAL OXIDATIVE PATHWAY INMUCOR-ROUXII

Mitochondria from spores, anaerobic yeasts and aerobic mycelium of Muc or rouxii were isolated and the components of the respiratory pathways were analysed. Our data suggest the presence in these mitochondria of three different NADH dehydrogenases, three b- and two c-type cytochro mes, plus three different terminal oxidases: cytochrome c oxidase, an incompletely characterized cytochrome which, by its spectral character istics, behaves as a cytochrome o, and a salicylhydroxamic-acid-sensit ive oxidase. The composition of the respiratory chain, as well as the relative proportions of cytochromes and oxidases in the mitochondria, were distinct at each developmental stage. Our data suggest that the d evelopment of the respiratory pathways during differentiation is mainl y regulated by the oxygen tension. Besides this role, oxygen also infl uences the relative number of mitochondria in the cells and their ultr astructural organization.