Iso-1-cytochromes c having lysine 32 replaced by leucine, glutamine, tyrosine, and tryptophan were prepared from strains of bakers' yeast, Saccharomyces cerevisiae, and chemically blocked at cysteine 107 with methyl methanethiolsulfonate to prevent dimerization. These modified ferricytochromes c were guanidine denatured, and the unfolding thermodynamics were determined by circular dichroism and...

Dansyl-to-heme distance distributions [P(r)] during folding have been determined in five variants of Saccharomyces cerevisiae iso-1 ferricytochrome c (labeled at mutant Cys residues 4, 39, 50, 66, and 99) by analysis of fluorescence energy-transfer kinetics. Moment analysis of the P(r) distributions clearly indicates that cytochrome c refolding is not a simple two-state process. After 1 ms of f...

Ustilago sphaerogena is a smut fungus which is parasitic on the grass Echinochloa crus-galli but may be cultured saprophytically in the sporidial stage of its life cycle. The form, rate of growth, and color of the sporidia were found (29) to be dependent upon the medium in which the fungus is grown. In a medium containing 2 % yeast extract and 2 % sucrose, large, rapidly growing pink sporidia w...

Cytochrome c oxidase (ferrocytochrome c: oxygen oxidoreductase, EC 1.9.3.1) was purified from the cytoplasmic membrane of the bacterium Paracoccus denitrificans. The enzyme contains two heme groups (a and a3) and two copper atoms per minimal unit, oxidizes mammalian cytochrome c at a high rate, and, when incorporated into liposomes, generates an electrochemical proton gradient during cytochrome...

The cytochrome c oxidase (COX) is the terminal enzyme of the respiratory chain. The complex accepts electrons from cytochrome c and passes them onto molecular oxygen. This process contributes to energy capture in the form of a membrane potential across the inner membrane. The enzyme complex assembles in a stepwise process from the three mitochondria-encoded core subunits Cox1, Cox2 and Cox3, wh...

The classic spectrophotometric method for identification and characterization of respiratory enzymes has been used for the study of the cytochrome system of Aplysia. Particles have been prepared from the buccal mass and the gizzard muscles. Difference spectra taken on isolated particle suspensions show the presence of a complete cytochrome system composed of five components: cytochrome a, b, c,...

HE cytoplasmic factor ( p ) and many nonallelic chromosomal genes determine the presence of cytochromes in yeast (EPHRUSSI 1953; GUNGE 1966; SHERMAN 1963). Ordinarily, a respiration-deficient (RD) mutant defective in any of these determinants lacks cytochromes a and b, but possesses cytochrome c at a normal or increased level, when grown aerobically. Recently, some mutant yeasts have been repor...

We have investigated the interaction between monomers of the dimeric yeast cytochrome bc(1) complex by analyzing the pre-steady and steady state activities of the isolated enzyme in the presence of antimycin under conditions that allow the first turnover of ubiquinol oxidation to be observable in cytochrome c(1) reduction. At pH 8.8, where the redox potential of the iron-sulfur protein is appro...

Cytochrome c release from mitochondria induces caspase activation in cytosols; however, it is unclear whether the redox state of cytosolic cytochrome c can regulate caspase activation. By using cytosol isolated from mammalian cells, we find that oxidation of cytochrome c by added cytochrome oxidase stimulates caspase activation, whereas reduction of cytochrome c by added tetramethylphenylenedia...