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Plant and Cell Physiology, 1962, Vol. 3, No. 1 23-42
© 1962

Article

HYDROGENASE REACTIONS IN RHODOPSEUDOMONAS PALUSTRIS

SEIKICHI IZAWA1

Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo

1. The hydrogenase reactions in a purple non-sulfur bacterium, Rhodopseudornonas palustris, were investigated. Under photoheterotrophic culturing conditions, the photosynthetic activity of the cells was found to be closely paralleled by the activity of hydrogenase. It was also revealed that the bacterium can grow under such conditions even withont both photosynthetic and the enzyme activities.

2. The enzyme was revealed to be localized in the particulate fraction (presumably chromatophores) of the disintegrated cells. The properties of the enzyme in the cell-free preparation and in intact cells were described.

3. Among various hydrogen acceptors tested, p-benzoquinone was most rapidly hydrogenated. Some heat-labile factor was shown to be involved in the reduction of quinone, which was not required in the reduction of methylene blue.

4. The reactions of hydrogenase, both in cell-free state (quinone- and MB-reduction) and in intact cells (oxyhydrogen reaction), were markedly inhibited by molecular oxygen. The inhibition was noncompetitive with respect to H2. A reversible mole-to-mole combination of the enzyme and O2 was suggested as the mechanism of the inhibition.

5. Carbon monoxide inhibition was suggested also to be caused by a reversible mole-to-mole combination of the enzyme and the inhibitor. This inhibition was competitive with respect to H2.

6. Rhodopseudomonas palustris hydrogenase was found to be refractory toward cyanide, azide and sulfhydryl reagents.

7. Light markedly suppressed the oxyhydrogen reaction (intact cells) whereas other hydrogenation reactions (intact cells and cell- free preparations) were not affected by illumination.

1Present address: Laboratory of Biological Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo.

(Received August 21, 1961; )
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