The biogenesis of the cyanellae of cyanophora paradoxa . I. Polypeptide composition of the cyanellae

Abstract

Based on polypeptide separation, protein purification and immunoblotting techniques using heterologous antibodies, we have been able to identify several photosynthetically important polypeptide components of the cyanellae of Cyanophora paradoxa . Cytochrome c -552 and ferredoxin have been purified to electrophoretic homogeneity and exhibit apparent molecular masses of 10.5 and 9.0 kDa, respectively. Cytochrome c -552 has an isoelectric point of pH 4.2±0.1. Plastocyanin was immunologically and spectrally undetectable even in cells grown in the presence of Cu 2+ . Polypeptides for cytochromes f , b -6 and c -552 have been located in electrophoretically resolved thylakoid samples by using the TMBZ-staining procedure. Intact phycobilisomes have been purified and characterized with respect to polypeptide composition and absorption and emission spectra. Photosystems I and II have been isolated and characterized with respect to their photochemical activities, spectral characteristics and polypeptide composition. Photochemically active PS I complexes fluoresce maximally at 720 nm at 77 K and comprise five polypeptide subunits resolved under denaturing conditions with apparent molecular masses of 66, 21, 18, 14 and 11 kDa. PS II core complexes mediate light-dependent 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-sensitive electron transfer between 1,5-diphenylcarbazide (DPC) and 2,6-dichlorophenolindophenol (DPIP) at rates of 140–200 μmol h -1 mg -1 chlorophyll. These complexes exhibit absorption maxima at 436 and 673 nm and show fluorescence emission maxima at 685 and 695 nm at 77 K. Rubisco was separated by two-dimensional electrophoresis and immunologically characterized.