Studies on cytochrome oxidase of yeast. I. Purification and enzymatic activity of cytochrome oxidase from saccharomyces oviformis M2

Construction of histidine-tagged yeast mitochondrial cytochrome c oxidase for facile purification of mutant forms

Yeast CcO (cytochrome c oxidase) has been developed as a facile system for the production and analysis of mutants of a mitochondrial form of CcO for mechanistic studies. First, a 6H tag (His6 tag) was fused to the C-terminus of a nuclear-encoded subunit of CcO from yeast Saccharomyces cerevisiae. This allowed efficient purification of a WT (wild-type) mitochondrial CcO, 6H-WT (yeast CcO with a 6H tag on the nuclear-encoded Cox13 subunit), with a recovery yield of 45%. Its catalytic-centre activity [≈180 e·s(-1) (electrons per s)], UV-visible signatures of oxidized and reduced states and ability to form the P(M) ['peroxy' (but actually a ferryl/radical state)] and F (ferryl) intermediates confirm normal functioning of the histidine-tagged protein. Point mutations were introduced into subunit I of the 6H-WT strain. All mutants were screened for their ability to assemble CcO and grow on respiratory substrate. One such mutant [6H-E243DI (the 6H-WT strain with an additional mutation of E243D in mitochondrial DNA-encoded subunit I)] was purified and showed ~50% of the 6H-WT catalytic-centre activity, consistent with the effects of the equivalent mutation in bacterial oxidases. Mutations in both the D and the H channels affect respiratory growth and these effects are discussed in terms of their putative roles in CcO mechanism.

Mitochondrial electron transport chain complex dysfunction in a transgenic mouse model for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease that causes degeneration of motoneurons. Mutation of Cu,Zn superoxide dismutase (SOD1) is one cause for this disease. In mice, expression of mutant protein causes motoneuron degeneration and paralysis resembling the human disease. Morphological change, indicative of mitochondrial damage, occurs at early stages of the disease. To determine whether mitochondrial function changes during the course of disease progression, enzyme activities of mitochondrial electron transport chain in spinal cords from mice at different disease stages were measured using three different methods: spectrophotometric assay, in situ histochemical enzyme assay, and blue native gel electrophoresis combined with in-gel histochemical reaction. The enzyme activities were decreased in the spinal cord, particularly in the ventral horn, beginning at early disease stages. This decrease persisted throughout the course of disease progression. This decrease was not detected in the spinal cords of non-transgenic animals, of mice expressing the wild-type protein, and in cerebellum and dorsal horn of the spinal cords from mice expressing mutant protein. These results demonstrate a functional defect in mitochondria in the ventral horn region and support the view that mitochondrial damage plays a role in mutant SOD1-induced motoneuron degeneration pathway.

Resonance Raman study of the aa3-type cytochrome oxidase of thermophilic bacterium PS3

Resonance Raman spectra of the aa3-type cytochrome oxidase of thermophilic bacterium PS3, which has a simpler subunit composition than the mitochondrial enzymes but very similar enzymatic properties, are investigated under various conditions and compared with those of mitochondrial enzymes. The intensities of the two marker lines of reduced cytochrome a3 at 1667 and 213 cm-1 had different dependences on the incubation temperatures and pH. With regard to the incubation temperature dependence, the intensity of the 1667-cm-1 line, the peripheral CH = O stretching mode of the a3 heme, behaved in nearly the same way as that of the oxidase activity whereas the intensity of the 213-cm-1 line, the Fe-histidine stretching mode of the a3 heme, exhibited a similar dependence to that of the proton pumping activity. The 213-cm-1 line disappeared upon binding of carbon monoxide, upon raising the pH above 9.2, or after incubating above 55 degrees C. The Raman line at 1611 cm-1, which was recently suggested to probe the proton pump activity [Babcock, G.T., & Callahan, P.M. (1983) Biochemistry 22, 2314-2319], remained unaltered after incubation at 60 degrees C for 20 min despite a reduction of proton pumping activity to one-third. This argues against the proposed mechanism. The frequencies of the Raman lines were the same for the intact membrane and the isolated enzyme in the reduced state. The Raman spectra of cytochrome oxidase isolated from bacterium, yeast, and bovine heart were different in the lower frequency region below 600 cm-1 but closely alike in the higher frequency region above 1200 cm-1.(ABSTRACT TRUNCATED AT 250 WORDS)

The partially reduced species present in purified cytochrome oxidase from baker's yeast is cytochrome a

Cytochrome oxidase purified from baker's yeast submitochondrial particles is found to exist in a partially reduced state in the resting enzyme. Studies utilizing optical and EPR spectroscopy indicate that the "inactive" fraction contains a reduced low-spin heme, cytochrome a possibly indicating a block of electron transfer from cytochrome a to cytochrome a 3. There is no apparent reduction of either the EPR-detectable copper or the species associated with the 830 nm band. Oxidative titrations of the resting-state yeast cytochrome oxidase indicate that the reduction potential of the species titrating is higher than that of ferricyanide. This "inactive" cytochrome oxidase is not the result of the isolation procedure, but seems to represent a species which is present in the intact yeast.

Cytochrome b-565 in Saccharomyces cerevisiae: use of mutants in the cob-box region of the mitochondrial DNA to study the functional role of this spectral species of cytochrome b. 1. Measurements of cytochromes b-562 and b-565 and selection of revertants devoid of cytochrome b-565

In order to study the functional role of the spectral species of cytochrome b-565 observed in mitochondria, genetically manipulated strains of Saccharomyces cerevisiae have been used. Strains have been found which are devoid of cytochrome b-565 under certain conditions and which nevertheless are able to grow on a respirable substrate. Two different methods have been used to determine the cytochrome b-565 content: anaerobic titrations and antimycin-A-induced reduction of cytochrome b-565. Both yield the same results.