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Plant Physiology 98:1285-1289 (1992)
© 1992 American Society of Plant Biologists

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Metabolism and Enzymology

Functional Importance of Arginine 64 in Chlamydomonas reinhardtii Phosphoribulokinase

Keith R. Roesler1, Beverly L. Marcotte and William L. Ogren

Department of Agronomy, University of Illinois, Urbana, Illinois 61801-3838, Department of Plant Biology, University of Illinois, Urbana, Illinois 61801-3838, Photosynthesis Research Unit, Agricultural Research Service, sUnited States Department of Agriculture, Urbana, Illinois 61801-3838

Phosphoribulokinase (EC 2.7.1.19) was investigated in wild-type Chlamydomonas reinhardtii and in mutant strains deficient in this enzyme activity. Immunoblot analysis revealed substantial amounts of phosphoribulokinase in mutant 12-2B but none in mutant F-60. The pH optimum of the wild-type enzyme was 8.0 and that of the 12-2B enzyme was 6.5. The mutant kinase possessed a Km value for ribulose 5-phosphate of about 45 millimolar, nearly three orders of magnitude greater than the wild-type value of 56 micromolar. Km values for ATP in the range of 36 to 72 micromolar were observed with both wild-type and mutant enzymes. The Vmax of the wild-type enzyme was about 450 micromoles per minute per milligram of protein, and values for the mutant enzyme were 140 micromoles per minute per milligram at pH 6.5 and 36 micromoles per minute per milligram at pH 7.8. Thermal stabilities of the wild-type and mutant kinases were similar. Sequence analysis of the 12-2B phosphoribulokinase gene revealed a C to T transition that caused an arginine to cysteine change at position 64 of the enzyme. This arginine residue is conserved in phosphoribulokinases from vascular plants, algae, and photosynthetic bacteria and appears to function in binding ribulose 5-phosphate.

1 Present address: Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824.




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E. Graciet, S. Lebreton, and B. Gontero
Emergence of new regulatory mechanisms in the Benson-Calvin pathway via protein-protein interactions: a glyceraldehyde-3-phosphate dehydrogenase/CP12/phosphoribulokinase complex
J. Exp. Bot., June 1, 2004; 55(400): 1245 - 1254.
[Abstract] [Full Text] [PDF]


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Copyright © 1992 by the American Society of Plant Biologists