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Plant and Cell Physiology, 1979, Vol. 20, No. 1 233-241
© 1979

Article

Effect of oxygen on photosynthesis and biosynthesis of glycolate in photoheterotrophically grown cells of Rhodospirillum rubrum1

Tetsuko Takabe2, C. B. Osmond2,3, R. E. Summons3 and T. Akazawa2

2Research Institute for Biochemical Regulation, School of Agriculture, Nagoya University Chikusa, Nagoya 464, Japan
3Department of Environmental Biology, Research School of Biological Sciences, Australian National University Canberra, Australia

Photosynthetic CO2 fixation was studied using cells of Rhodospirillum rubrum grown heterotrophically on malate or butyrate. Rates of CO2 fixation were higher in the malategrown cells than in the butyrate-grown bacteria but ribulosebisphosphate (RUP2) carboxylase/oxygenase activities were higher in the extracts prepared from the butyrate-grown bacteria. The photosynthetic CO2 fixation in the butyrate-grown R. rubrum cells was inhibited by KCN, and the inhibitory effect of O2 on CO2 fixation was reversed when cells were returned to an N2 atmosphere. In the malate-grown cells, photosynthetic CO2 fixation was insensitive to KCN and the inhibitory effect exerted by O2 was practically irreversible.

14CO2 was not incorporated into glycolate by either malate- or butyrate-grown cells in an N2 atmosphere, but small amounts of labeled glycolate were found in malate- and butyrate-grown cells in air or 100% O2. Glycolate excreted by these cells in 100% O2 was measured colorimetrically and its identity established by mass spectrometry. When the O2 atmosphere was labeled with 18O2, only one of the carboxyl oxygens of the excreted glycolate was labeled, and the enrichment of 18O in this carboxyl oxygen relative to the 18O2 provided was greater than 80%. These studies show that significant glycolate production by R. rubrum only occurs in the presence of O2 and that in both malateand butyrate-grown cells, the glycolate so formed is presumably produced via RuP2 oxygenase.

1 Paper No. 46 in the series "Structure and Function of Chloroplast Proteins", and research supported in part by research grants from the Japanese Ministry of Education (No. 211113), the Toray Science Foundation (Tokyo), and the Nissan Science Foundation (Tokyo).

(Received August 19, 1978; )
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