Mitochondrial oxidase systems of Neurospora crassa were investigatedwith respect to their mechanisms of electron transport and theirrelationships to respiratory metabolism.
A mitochondrial oxidase system able to utilize dihydroorotic acidas a primary substrate was found and characterized. Another substratefor this system was isolated from yeast extract and identified as 5-N-methylformamido-L-dihydroorotic acid. This system was found to occurin both wildtype and poky, a respiratory mutant. No linkage to thecytochrome chain or to oxidative phosphorylation could be detected.
A succinate oxidase system and NADH oxidase system independent ofcytochromes b,a, and a3 were found to occur in both wildtype and inthe poky mutant. The system was partially characterized using thepoky mutant, which is deficient in cytochromes b,a and a3.It was found that this oxidase system was a part of respiratory metabolism andwas linked to oxidative phosphorylation.
Mechanisms of electron transport in these oxidase systems are discussedand models presented.
Possible biological origins and the biological significance of5 N-methylformamidodihydroorotic acid are also discussed.
The development of poky and wildtype mitochondria during the growthcycle were studied and compared. Differences in morphology were detectedusing electron microscopy and differences in cytochrome content weredetected by absorption spectroscopy. The relationships between the oxidasesystems and mitochondrial development are discussed.
