title: Calvin cycle multienzyme complexes are bound to chloroplast thylakoid membranes of higher plants in situ.
abstract: Further evidence is provided that the Calvin cycle enzymes ribose-5-phosphate isomerase (EC 5.3.1.6), ribulose-5-phosphate kinase (Ru-5-P-K, EC 2.7.1.19), ribulose-1,5-bisphosphate carboxylase (RuP2Case, EC 4.1.1.39), glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12), sedoheptulose-1,7-bisphosphatase (Sed-1,7-bPase, EC 3.1.3.37), and electron transport protein ferredoxin-NADP+ reductase (FNR, EC 1.18.1.1) are organized into stable CO2-fixing multienzyme complexes with a molecular mass of 900 kDa. Limited trypsinolysis combined with immunoblotting revealed that all of chloroplast stromal Ru-5-P-K and GAPDH is located in enzyme complexes. The Calvin cycle enzyme complexes remain intact indefinitely at lower ionic strength but dissociate into components at KCl concentrations >250 mM. Immunoelectron microscopy showed that Ru-5-P-K, GAPDH, Sed-1,7-bPase, and FNR are bound to stroma-faced thylakoid membranes in situ, whereas RuP2Case and RuP2Case activase are randomly distributed throughout chloroplasts. The results indicate that membrane-bound enzyme supercomplexes may play an important role in photosynthesis.
authors.affiliation: Institute of Plant Genetics and Crop Plant Research, Gatersleben, Federal Republic of Germany.
authors.forename: K H
authors.initials: KH
authors.lastname: Suss
authors.forename: C
authors.initials: C
authors.lastname: Arkona
authors.forename: R
authors.initials: R
authors.lastname: Manteuffel
authors.forename: K
authors.initials: K
authors.lastname: Adler