Hydrogen and Proton Transfer Across the Chloroplast Envelope

Abstract

The chloroplast stroma is separated from the cytoplasmic compartment of leaf cells by the chloroplast envelope which exerts control functions in leaf metabolism in that it permits passage of some metabolites, but not of others. The chloroplast envelope has been found to be practically impermeable to oxidized and reduced pyridine nucleotides (HEBER & SANTARIUS 1965, ROBINSON & STOCKING 1968, MATHIEU 1967). Still, some communication between chloroplastic and cytoplasmic redox potentials does exist. In this contribution indirect transfer of hydrogen across the chloroplast envelope via cyclic transport metabolite systems is discussed. Proton transfer across the chloroplast envelope is also considered, since protons are reactants in redox reactions which form part of indirect transfer systems.