Light Activation of Pyruvate, Orthophosphate Dikinase in Maize Mesophyll Chloroplasts: A Role for Adenylate Energy Charge |
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Authors: | Nakamoto, Hitoshi Young, Park Shin |
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Affiliation: | Radioisotope Centre, The University of Tokyo 2-11-16, Yayoi, Bunkyo-ku, Tokyo, 113 Japan |
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Abstract: | Pyruvate, orthophosphate dikinase (EC 2.7.9.1[EC]) was activatedin the light and inactivated following a dark treatment in intactmaize mesophyll chloroplasts. Addition of catalase (100250units/ml) to the assay medium was necessary to obtain good activationand to keep the enzyme in an active state during illumination.Arsenate and carbonyl cyanide m-chlorophenyl-hydrazone, uncouplersof photophosphorylation, inhibited the activation. Pyruvate,which has been proposed to have a critical role in supportingthe light activation of pyruvate, orthophosphate dikinase, actuallyinhibited the activation. The pyruvate level in the chloroplastsuspension decreased when the enzyme was light-activated. Measurementsof adenylates and pyruvate in the chloroplasts indicated thatthe energy state of the chloroplasts was more important forthe light activation than was the level of pyruvate. 1Present address: Department of Biochemistry, Faculty of Science,Saitama University, 255, Shimo-Okubo, Urawa, 338 Japan2Present address: National Institute of Agrobiological Resources,Yatabe, Tsukuba, Ibaraki, 305 Japan (Received May 2, 1989; Accepted October 2, 1989) |
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