1995 Fiscal Year Final Research Report Summary

Electron transfer proteins of chloroplast envelope

Research Project

Project/Area Number	06640853
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	植物生理
Research Institution	Osaka Prefecture University
Principal Investigator	TAKAHASHI Masaaki Osaka Prefecture University, Department of Applied Biological Chemistry, Professor, 農学部, 教授 (30027198)
Project Period (FY)	1994 – 1995
Keywords	spinach / intact chloroplast / envelope / Cytochrome c / electron transfer / photophosphorylation
Research Abstract	We found the reduction of extrachloroplastic cytochrome (Cyt) c by illuminated intact chloroplasts. This reaction was mediated by a trans-envelope electron transfer but not by soluble reductants generated in stroma such as superoxide, hydrogen peroxide or NAD(P)H.By the use of the oxidation of the reduced Cyt c, re-dox substance was identified as a multimeric complex of proteins with substance (s) with E^<o1> which is similar to that of plastoquinone. The redox substances are localized both in outer and inner envelopes. Cyt c reduction by intact chloroplast was inhibited by DCMU but not by DBMIB which indicates that the envelope electron transfer accepts electrons from the plastoquinone site in the photosynthetic electron transfer. The rates of carbon dioxide fixation and carbon dioxide-dependent oxygen evolution were lowered by the addition of Cyt c. Cyclic and noncyclic photophosphorylations by thylakoid membranes were suppressed by the addition of isolated envelope membranes. These declines in photosynthetic activities were not the result of dissipation of electrons to Cyt c through envelope electron transfer because the reduced amount of Cyt c was much lesser than the decreased yield of oxygen evolution. Envelope electron transfer might be a unique reaction which equalizes the photosynthetic yield between thylakoids and/or chloroplasts.