The electron transport components of wild type and poky strains of Neurospora crassa.

A detailed spectrophotometric study was made of the electron transport systems in .mitochondria from wild type and poky strains of Neurospora crassa. Wild type mitochondria were found to contain flavoproteins, two b-type cytochromes (G-peaks (77%) at 554 and 561 nm), two c-type cytochromes (a-peaks (77°K) at 545 and 550 nm), and cytochrome (1~73 (a-peak (77°K) at 601 nm). In terms of their spectra, the band c-type cytochromes of poky mitochondria are identical with those of wild type; the room temperature absorption minimum of poky flavoproteins is shifted from 460 (the wild type value) to 451 nm, however, and the a-peak (77°K) of poky cytochrome aa3 is shifted from 601 to 591 nm. The most striking difference between wild type and poky lies in the concentrations of the electron carriers. Poky mitochondria contain flavoproteins and cytochrome c (largely ~545) at 30% higher concentrations than wild type mitochondria, but are grossly deficient in band a-type cytochromes. Furthermore, the concentration ratio, cytochrome aa3 to cytochrome b, is about 0.3 in poky compared with 1.0 in wild type mitochondria, a fact which probably accounts for relatively high steady state levels of reduction of cytochrome c in poky mitochondria. Enzymatic determinations of pyridine nucleotides showed NAD+ and NADH to predominate over NADP+‘ and NADPH in mitochondria from both strains. The total concentration of pyridine nucleotides in poky was about one-half that in wild type. In addition to the cytochrome chain, poky is known to possess an alternate, cyanide-insensitive oxidase system. The present experiments show that none of the cytochrome components of poky mitochondria plays any direct role in this system.