Plant Physiol. Drug Metab Dispos
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Plant Physiology 100:1361-1365 (1992)
© 1992 American Society of Plant Biologists

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Metabolism and Enzymology

Coupling of Carbon Dioxide Fixation to the Oxyhydrogen Reaction in the Isolated Chloroplast of Chlamydomonas reinhardtii1

Changguo Chen2 and Martin Gibbs

Institute for Photobiology of Cells and Organelles, Brandeis University, Waltham, Massachusetts 02254

The oxyhydrogen reaction (the reduction of O2 to water by H2) in the presence of CO2 was studied in the isolated Chlamydomonas reinhardtii chloroplast by monitoring the rate of 14CO2 incorporation into acid-stable products in the dark. The endogenous rate of CO2 uptake (50-125 nmol/mg chlorophyll per h) was increased about 3- to 4-fold by ATP and additionally when combined with glucose, ribose-5-phosphate, and glycerate-3-phosphate. The rate was diminished 50 to 75%, respectively, when H2 was replaced by N2 or by air. Decrease in CO2 uptake by DL-glyceraldehyde was taken to indicate that the regenerative phase and complete Calvin cycle turnover were involved. Diminution of CO2 incorporation by rotenone, antimycin A, and 2,5-dibromo-3-methyl-6-isopropanol-p-benzoquinone was attributed to an inhibition of the oxyhydrogen reaction, resulting in an elevated NADPH/NADP ratio. If so, then the diminished CO2 uptake could have been by "product inhibition" of the carbon metabolic network. Our data are consistent with the proposal (H. Gaffron [1942] J Gen Physiol 26: 241-267) that CO2 fixation coupled to the oxyhydrogen reaction is dependent to some extent on exchloroplastic metabolism. This support is primarily ATP provided by mitochondrial respiration.

2 Present address: N-212 Agricultural Science N, University of Kentucky, Lexington, KY 40546-0001.

1 Supported by U.S. Department of Energy DE.FG02-86ER 13486.






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Copyright © 1992 by the American Society of Plant Biologists