Neurospora cytochrome

The data presented in Table 3, which includes the amino acid composition of baker s yeast and Candida krusei cytochrome c for comparison, show that Ustilago and Neurospora cytochrome c contain the same number of total residues. In seven instances, the number of residues of a particular amino acid/mole are identical. Thus, even in the absence of a sequence for the Ustilago cytochrome it can be concluded that this protein, unlike the siderochromes, has suffered little alteration in the progression from the Ascomycetes to the Basidiomycetes. This can be ascribed to the varying function of the two types of molecules. Cytochrome c must fit into a relatively specific slot bounded by a reductase and an oxidase and it has hence evolved much more slowly than the more freely acting transport agents where the specificity constraints are less demanding. 

Residue 72 is in a region which is invariant in plant and microbial cytochrome c s and residue 86 is in a region which is characterized in almost all cytochromes as being either Lys-Lys or Lys-Lys-Lys. Neurospora cytochrome c contains c-N-trimethyllysine at residue 72 only, and animal and most plant cytochrome c s are not methylated. 

A further promising attempt to identify the bluelight-reducible cyt b is described by Britz et al.26) for a plasma-membrane-enriched fraction of com coleoptiles. They find that methylene blue (Scheme 2) is capable of reducing a particular cyt b which constitutes only 10—20% of the total dithionite-reducible cytochromes. Since this particular cyt b is very similar to that which is photo-reduced by endogeneous flavin in Neurospora 122,123) the two are proposed to be identical. 

LS, K.H.D. Lederer, F. (1983). On the presence of a heme-binding domain homologous to cytochrome b5 in Neurospora crassa assimilatory nitrate reductase. The EMBO Journal 2, 1909-14. 

The assimilatory enzyme from the mold Neurospora crassa has been intensively studied for over two decades, particularly by Nason and his collaborators. Thus, Nason and Evans (39) identified FAD as a prosthetic group in the enzyme Nicholas, Nason, and McElroy (40) showed that molybdenum was required for the synthesis of nitrate reductase Nicholas and Nason (41) suggested its presence in the enzyme Garrett and Nason (42) showed that a b-type cytochrome (cytochrome 6557) co-purifies with this nitrate reductase and Nason et al. (11) suggested, from in vitro complementation experiments with nitrate reductaseless mutants, that the enzyme consists of at least two components required for activity. These workers have suggested that the electron transfer pathway is ... 

Draw an evolutionary tree for the human, rabbit, silkworm, and Neurospora (fungus) by using the data in the following table for differences in the respective cytochrome c sequence. 

These data allow us to construct an evolutionary tree, with branch lengths approximately proportional to the number of differences between the species (see Fig. 4-10). The human and rabbit show most similarity and therefore are connected by short branches. The silkworm cytochrome c is closer to both mammalian forms than it is to Neurospora, and so should be connected to the mammalian junction. The length of the silkworm branch will be approximately three times the length of the rabbit and human branches. Finally, Neurospora shows approximately the same number of differences with all the animal species, and therefore can be joined to their common branch. 

Li, Y., Leonard, K., and Weiss, H., 1981, Membranenbound and water-soluble cytochrome c, Neurospora mitochondria, Eur. J. Biochem. 116 199n205. 

Weiss, H., and Kolb, H. J., 1979, Isolation of mitochondrial succinate ubiquinone reductase, cytochrome c reductase and cytochrome c oxidase from Neurospora crassa using nonionic detergent, Eur. J. Biochem. 99 139nl49. 

From the primary structures bovine cytochrome c, [181], human [182], bovine [153], mouse [183], Saccharomyces [184], Aspergillus [185], and Neurospora [186] cytochrome b. Studies on the bovine [187] and Neurospora [188,189] Complex III are summarised. Complex III from rat [190] and Saccharomyces [191] are very similar but the latter may lack the smallest subunit , band VIII [192]. The complex forms dimers in Triton X-100 [189,192,193]. 

The core proteins and the Rieske FeS protein can be dissociated from Triton X-lOO-solubilised cytochrome c reductase in concentrated NaCl. The cytochrome core was isolated from the dissociated Complex III of Neurospora by gel filtration [230]. It retains most of the hydrophobic character of the parent protein and seems to correspond to the membrane-embedded part of Complex III. 

NDMA is mutagenic for Escherichia coli, Salmonella typhimurium, and Neurospora crassa. It can produce mitotic recombination in Sacharoyus cerevesiae species, recessive lethal mutations in Drosophilla melanogaster, and chromosomal aberrations in mammalian cells. Mutagenic responses in bacterial cells are dependent upon the addition of a mammalian drug metabolism system (specific form of cytochrome P450). 

Just as with protein (arginine) methyltransferase, it is likely that there are several protein (lysine) methyltransferases. Neurospora and wheat germ cytochrome cs contain only c-N-trimethyllysine (196), while pea embryo histone III and bovine retina opsin contain either c-N-mono-or c-N-dimethyllysine, but not c-N-trimethyllysine (211). Flagella protein from Salmonella serpens contains only c-N-monomethyllysine (212). 

Attar, R.M., E. Grotewold, G.E. Taccioli, G.O. Aisemberg, H.N. Torres, and N.D. Judewicz (1989). A cycloheximide-inducible gene of Neurospora crassa belongs to the cytochrome P450 superfamily Nucleic Acids Res. 17, 7535-7536. 

There are no plasma membrane-bound enzymes whose activities are known to be specifically and sufficiently altered to account for growth Inhibition by the sterol inhibitors at sub-MIC doses. A likely candidate is chitin synthetase, but the activity of this enzyme is not reduced in fact, sterol inhibitor-treated fungi contain more glucosamine polymers than controls. However, the altered deposition of chitin (see above references) may reflect a discontinuity between cytoskeletal elements which are believed to be involved in cell wall formation and the plasma membrane, but it is unlikely that this is at the root of growth inhibition since a wall-less slime mutant of Neurospora crassa is as sensitive as the wild-type strain to propiconazole (57TI Cytochrome oxidase and microsomal ATPase are inhibited by high concentrations (10 5,... 

Further data were obtained by Weiss et al. (1971) with Neurospora crassa. Chromatography of mitochondrial protein labeled in vivo in the presence of cycloheximide (CH), yielded fractions containing difilerent amounts of radioactivity. The fraction of highest specific radioactivity was pure and enzymically active cytochrome oxidase. Separation of the polypeptide chains of this enzyme by SDS gel electrophoresis revealed five protein bands of which, in the presence of CH, only one polypeptide was highly labeled. Similar results were obtained with cytochrome oxidase from Locusta migratoria (Weiss et al, 1972). Here seven polypeptide chains were obtained. One, with a molecular weight of about 19,000, was labeled in the presence of CH and may be a product of mitochondrial protein synthesis. 

N.r. of Neurospora crassa has M, 228,000. A N.r. mutant (Neurospora crassa nit-3) produces a subunit of N.r. containing cytochrome and Mo (M, 160,000) this does not react with NAD(P)H, but transfers electrons to nitrate from exogenous FADH2 or reduced methyl viologen. The other component is produced by Neurospora crassa nit-I it is unable to reduce nitrate, but catalyses the reduction of cytochrome c by NAD(P)H. 

Neurospora, like yeast, has nuclear genes that appear to be involved in cytochrome biosynthesis. For example, Neurospora mutant Cl 17 lacks cytochrome c, whereas mutant C115 contains more cytochrome c than does the wild type, but does not contain cytochrome a [43,44]. A nuclear suppressor gene is known which restores the cytochrome system of Cl 15 [44]. 

The possibility that the cytoplasmically inherited defect in poky reflects an altered structural protein has been explored [80] and questioned [81,82]. Recent experiments have suggested that the phenotype of poky is attributable to an imbalance in the synthesis of mitochondrial ribosomal subunits resulting in a relative lack of mitochondrial ribosome monomers and thus in a reduction of intrinsic protein synthesis, with a consequent effect on cytochrome content [82]. The characteristic mitochondrial ribosomes of normal Neurospora strains had previously been studied and recognized as components of the intrinsic protein-synthesizing machinery [83,84]. 

---