The isoforms of yeast cytochrome c oxidase subunit V alter the in vivo kinetic properties of the holoenzyme.
One of the nuclear-coded subunits of yeast cytochrome c oxidase is specified by a gene family composed of two genes, COX5a and COX5b. These genes are regulated differentially by oxygen and encode isoforms of subunit V, designated Va and Vb, which have only 66% primary sequence identity. Yeast cells require one or the other isoform for a functional cytochrome c oxidase (Trueblood, C. E., and Poyton, R. O. (1987) Mol. Cell Biol. 7, 3520-3526). To determine if these isoforms of subunit V alter the catalytic properties of holocytochrome c oxidase, we have analyzed various aspects of cytochrome c oxidase function in intact yeast cells that produce only one type of isoform. From measurements of room temperature turnover numbers and low temperature rates of ligand binding, single turnover cytochrome c oxidation, and internal electron transfer (heme a oxidation), we have found that isozymes which incorporate the Vb isoform have both higher turnover rates and higher rates of heme a oxidation than isozymes which incorporate Va. These findings support the conclusion that the isoforms of subunit V modulate cytochrome c oxidase activity in vivo and suggest that they do so by altering the rates of one or more intramolecular electron transfer reactions.
Waterland
R A
RA
Department of Biochemistry and Biophysics, University of Pennsylania, Philadelphia 19104.
Basu
A
A
Chance
B
B
Poyton
R O
RO
D002248:Carbon Monoxide / Q000378:metabolism; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D046911:Macromolecular Substances; D010100:Oxygen / Q000378:metabolism; D011048:Polarography; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013057:Spectrum Analysis; D013329:Structure-Activity Relationship; D013696:Temperature
D007527:Isoenzymes; D046911:Macromolecular Substances; D002248:Carbon Monoxide; D003576:Electron Transport Complex IV; D010100:Oxygen