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Articles

Enzyme Regulation in C₄ Photosynthesis ¹

Identification and Localization of Activities Catalyzing the Synthesis and Hydrolysis of Fructose-2,6-Bisphosphate in Corn Leaves

Division of Molecular Plant Biology, Hilgard Hall, University of California, Berkeley, California 94720

Activities catalyzing the synthesis of fructose-2,6-bisphosphate (fructose-6-phosphate,2-kinase or Fru-6-P,2K) and its breakdown (fructose-2,6-bisphosphatase or Fru-2,6-P₂ase) were identified in leaves of corn (Zea mays), a C₄ plant. Fru-6-P,2K and Fru-2,6-P₂ase were both localized mainly, if not entirely, in the leaf mesophyll cells. A partially purified preparation containing the two activities revealed that the kinase and phosphatase were regulated by metabolite effectors in a manner generally similar to their counterparts in C₃ species. Thus, corn Fru-6-P,2K was activated by inorganic phosphate (Pi) and fructose-6-phosphate, and was inhibited by 3-phosphoglycerate and dihydroxyacetone phosphate. Fru-2,6-P₂ase was inhibited by its products, fructose-6-phosphate and Pi. However, unlike its spinach equivalent, corn Fru-2,6-P₂ase was also inhibited by 3-phosphoglycerate and, less effectively, by dihydroxyacetone phosphate. The C₄ Fru-6-P,2K and Fru-2,6-P₂ase were also quite sensitive to inhibition by phosphoenolpyruvate, and each enzyme was also selectively inhibited by certain other metabolites.

³ Present address: Botanisches Institut der Universität Köln, II. Lehrstuhl, Gryhofstrasse 15, D-5000 Köln 41, F.R.G.

¹ Supported by a grant-in-aid from Chevron Chemical Company. Fifth paper of a series. The earlier papers are identified in Jacquot JP, P Gadal, AN Nishizawa, BC Yee, NA Crawford, BB Buchanan 1984 Arch Biochem Biophys 228: 170-178. A preliminary account of this work has been published (Soll J, J Wötzel, BB Buchanan, 1983. Sixth International Congress on Photosynthesis, Abstracts, Brussels, Belgium, 1983, pp 112-128).