Effects of a transition from normoxia to anoxia on yeast cytochrome c oxidase and the mitochondrial respiratory chain: implications for hypoxic gene induction.
Previous studies have demonstrated that the mitochondrial respiratory chain and cytochrome c oxidase participate in oxygen sensing and the induction of some hypoxic nuclear genes in eukaryotes. In addition, it has been proposed that mitochondrially-generated reactive oxygen and nitrogen species function as signals in a signaling pathway for the induction of hypoxic genes. To gain insight concerning this pathway, we have looked at changes in the functionality of the yeast respiratory chain as cells experience a shift from normoxia to anoxia. These studies have revealed that yeast cells retain the ability to respire at normoxic levels for up to 4 h after a shift and that the mitochondrial cytochrome levels drop rapidly to 30--50% of their normoxic levels and the turnover rate of cytochrome c oxidase (COX) increases during this shift. The increase in COX turnover rate cannot be explained by replacing the aerobic isoform, Va, of cytochrome c oxidase subunit V with the more active hypoxic isoform, Vb. We have also found that mitochondria retain the ability to respire, albeit at reduced levels, in anoxic cells, indicating that yeast cells maintain a functional mitochondrial respiratory chain in the absence of oxygen. This raises the intriguing possibility that the mitochondrial respiratory chain has a previously unexplored role in anoxic cells and may function with an alternative electron acceptor when oxygen is unavailable.
David
Pamela S
PS
The Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309-0347, USA.
Poyton
Robert O
RO
D000693:Anaerobiosis / Q000502:physiology; D003580:Cytochromes / Q000378:metabolism; D004579:Electron Transport; D003576:Electron Transport Complex IV / Q000378:metabolism*; D044943:Fatty Acid Desaturases / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D007527:Isoenzymes / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology*; D010100:Oxygen / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013230:Stearoyl-CoA Desaturase; D015533:Transcriptional Activation
D003580:Cytochromes; D007527:Isoenzymes; D029701:Saccharomyces cerevisiae Proteins; D044943:Fatty Acid Desaturases; D013230:Stearoyl-CoA Desaturase; C029627:delta-9 fatty acid desaturase; D003576:Electron Transport Complex IV; D010100:Oxygen