Studies of respiratory components and oxidative phosphorylation in mitochondria of mi-1 Neurospora crassa.
Oxidative phosphorylation has been demonstrated with mitochondria of the mi-1 respiratory mutant of Neurospora crassa. The P/O ratios observed with these mitochondria were approximately 0.8 with citrate and 0.4 with either externally added reduced nicotinamide adenine dinucleotide (NADH), succinate, or ascorbate-tetramethyl-p-phenylenediamine (TPD). These P/O ratios suggest that there are only two sites of phosphorylation in mitochondria isolated from young (20 to 24 h) cultures of the mi-1 mutant. The energy-dependent reduction of NAD(+) with succinate and the phosphorylation associated with ascorbate-TPD oxidation indicate that the first and the third sites of energy coupling are present in this mutant. Difference spectra of mitochondria from young cultures of the mi-1 mutant revealed the presence of cytochrome c. Cytochromes b and a + a(3) were not detected. However, in the presence of antimycin A, a small peak in the Soret region at 430 nm was observed. A carbon monoxide difference spectrum revealed the presence of a component of the respiratory chain with a spectrum similar to that of cytochrome o. It is of interest that respiratory inhibitors such as antimycin A, 2-n-nonylhydroxyquinoline N-oxide, and cyanide abolished phosphorylation but only partially inhibited oxidation. It is postulated that the mi-1 respiratory system contains two pathways of electron transport-the first is associated with a phosphorylating pathway, whereas the second is a non-phosphorylating electron transport pathway.
D000968:Antimycin A / Q000494:pharmacology; D001205:Ascorbic Acid / Q000378:metabolism; D002122:Calcium Chloride / Q000494:pharmacology; D002951:Citrates / Q000378:metabolism; D003486:Cyanides / Q000494:pharmacology; D003574:Cytochrome c Group / Q000378:metabolism; D004140:Dinitrophenols / Q000494:pharmacology; D004579:Electron Transport; D008365:Manometry; D008928:Mitochondria / Q000378:metabolism*; D009154:Mutation; D009243:NAD / Q000378:metabolism; D009491:Neurospora / Q000378:metabolism*; D009492:Neurospora crassa / Q000378:metabolism; D010084:Oxidation-Reduction; D010085:Oxidative Phosphorylation / Q000187:drug effects*; D010101:Oxygen Consumption; D010655:Phenylenediamines / Q000378:metabolism; D011804:Quinolines / Q000494:pharmacology; D012402:Rotenone / Q000494:pharmacology; D013053:Spectrophotometry; D013386:Succinates / Q000378:metabolism; D013447:Sulfites / Q000378:metabolism
D002951:Citrates; D003486:Cyanides; D003574:Cytochrome c Group; D004140:Dinitrophenols; D010655:Phenylenediamines; D011804:Quinolines; D013386:Succinates; D013447:Sulfites; D012402:Rotenone; D009243:NAD; D000968:Antimycin A; D002122:Calcium Chloride; D001205:Ascorbic Acid