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Plant Physiology 63:1138-1142 (1979)
© 1979 American Society of Plant Biologists

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Articles

Inactivation of Hydrogenase in Cell-free Extracts and Whole Cells of Chlamydomonas reinhardi by Oxygen 1

David L. Erbes, Dan King2 and Martin Gibbs

a Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts 02154

O2 irreversibly inactivates hydrogenase from Chlamydomonas reinhardi. The mechanism for the inactivation involves the reaction of one molecule of hydrogenase with one molecule of O2 (or two oxygen atoms) in the transition complex of the rate-limiting step. The second order rate constant for this reaction is 190 atmospheres–1 minute–1 (1.4 x 105 molar–1 minute–1). At levels above 0.01 atmosphere O2, the increased numbers of O2 molecules may compete for the site of inactivation hindering the proper orientation for inactivation of any one O2 molecule and resulting in lowered rates of inactivation.

CO is a reversible inhibitor of hydrogenase acting competitively against H2. The Ki for CO is 0.0010 atmosphere. CO antagonizes O2 inactivation. In a period when complete inactivation by O2 would usually occur, the presence of CO greatly reduces the inactivation rate.

After 3 hours of adaptation in whole cells, the presence of H2 lowers the rate of deadaptation of hydrogenase. Inasmuch as H2 promotes increased O2 uptake the cellular concentration of O2 is likely to be lower. After 48 hours of adaptation O2 uptake is reduced even when H2 is present and the pattern of deadaptation under O2 with and without H2 and CO is qualitatively the same as observed for the inactivation of cell-free hydrogenase. The mechanism of inactivation of cell-free hydrogenase by O2 may be the same as the mechanism for loss of hydrogenase during deadaptation in whole algal cells.

2 Present address: Department of Biology, Lycoming College, Williamsport, Pennsylvania 17701.

1 This research was supported by Department of Energy Grant EY-76-S-02-3231-14 and National Science Foundation Grant PCM76-82157.




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