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Metabolism and Enzymology

Purification and Characterization of Pea Chloroplastic Phosphoriboisomerase ^1,2

Department of Biological Sciences, University of Illinois at Chicago, Chicago Illinois 60680, Corporate Molecular Biology, Abbott Laboratories, Abbott Park, Illinois 60064, Avdelningen för Biokemi, Kemicentrum, Lunds Universitet, S-220 07 Lund, Sweden

Pea (Pisum sativum L.) chloroplastic phosphoriboisomerase (EC 5.3.1.6) can be purified to apparent homogeneity in less than 2 days time with a 53% yield. Important steps in the purification include heat treatment and pseudoaffinity chromatography on Red H-3BN Sepharose. The purified isomerase has a subunit molecular mass of 26.4 kD. The N-terminal sequence has been determined through 34 residues. pH optima are 7.8 (ribose-5-phosphate) and 7.7 (ribulose-5-phosphate); K_m values are 0.9 millimolar (ribose-5-phosphate) and 0.6 millimolar (ribulose-5-phosphate). The enzyme is inhibited by erythrose-4-phosphate, sedoheptulosebisphosphate, glyceraldehyde-3-phosphate, and 3-phosphoglycerate at concentrations close to those found in photosynthesizing chloroplasts. Countercurrent phase partitioning experiments indicate that the pea chloroplastic phosphoriboisomerase interacts physically with phosphoribulokinase.

¹ In memory of Professor Mordhay Avron.

² This work was supported in part by grants from the Department of Energy (FG02-85ER60367), the National Science Foundation (DBM 84 17081), and the University of Illinois at Chicago Research Board to L.E.A. and from the Swedish Natural Science Research Council to G.J. C.L.S. was a postdoctoral research fellow of the Laboratory for Cellular, Molecular, and Developmental Biology, University of Illinois at Chicago, and recipient of a Fellowship from the International Union of Biochemistry for travel to Sweden. I.M.G. was the recipient of a University of Illinois at Chicago Young Biologist Award funded by the Howard Hughes Medical Institute.