This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (69) Citing Articles via Google Scholar Google Scholar Articles by Chu, D. K. Articles by Bassham, J. A. Search for Related Content PubMed PubMed Citation Articles by Chu, D. K. Articles by Bassham, J. A. Agricola Articles by Chu, D. K. Articles by Bassham, J. A.

Articles

Activation of Ribulose 1,5-Diphosphate Carboxylase by Nicotinamide Adenine Dinucleotide Phosphate and Other Chloroplast Metabolites ¹

^a Laboratory of Chemical Biodynamics, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720

Ribulose 1,5-diphosphate carboxylase, when activated by preincubation with 10 mM MgCl₂ and 1 mM bicarbonate in the absence of ribulose 1,5-diphosphate, can be further activated about 170% with 0.5 mM NADPH present in the preincubation mixture. NADP⁺, NADH, and NAD⁺ are ineffective. The activation by NADPH is comparable to that previously seen with 0.05 to 0.10 mM 6-phosphogluconate in that these specific preincubation conditions are required, but the effects of NADPH and 6-phosphogluconate are not additive. Moreover, where higher concentrations of 6-phosphogluconate inhibited the enzyme, higher concentrations of NADPH give a greater activation, saturating at about 1 mM and 200%. Under the specified conditions of preincubation, fructose 1,6-diphosphate has an activation curve similar to that of 6-phosphogluconate, peaking at 0.1 mM and 70%. Above this level, activation decreases, and inhibition is seen at still higher concentrations. Other metabolites tested produced smaller or no effects on the enzyme activity assayed under these conditions. When either reduced NADP or 6-phosphogluconate are present in the preincubation mixture, it becomes possible to determine the Km for bicarbonate using a Lineweaver-Burk plot, and the Km for bicarbonate under these conditions is 2.8 mM, corresponding to 0.3% CO₂ at pH 7.8 and 25 C.

This article has been cited by other articles:

				J. A. Bassham Increasing Crop Production Through More Controlled Photosynthesis Science, August 12, 1977; 197(4304): 630 - 638. [PDF]