Portal de Periódicos da CAPES

Protein synthesis in isolated spinach chloroplasts: Comparison of light-driven and ATP-driven synthesis

1974; Elsevier BV; Volume: 164; Issue: 1 Linguagem: Inglês

10.1016/0003-9861(74)90012-5

1096-0384

W. Bottomley, Donald Spencer, Paul R. Whitfeld,

Mitochondrial Function and Pathology

A comparison has been made of the optimal concentrations of Mg2+ and K+ ions necessary for both light-driven protein synthesis in intact spinach chloroplasts and for ATP-driven protein synthesis in broken chloroplasts, and the products of the two systems have been compared by polyacrylamide gel electrophoresis. Light-driven incorporation of amino acids into polypeptides in intact chloroplasts assayed in buffer systems containing sucrose or sorbitol as the osmoticum is inhibited by the addition of Mg2+, the effect being most marked at low concentrations (less than 40 mm) of KCl. On the other hand, chloroplasts suspended in 0.2 m KCl as osmoticum require Mg2+ (3 mm) for optimal light-driven protein-synthesizing activity. Incorporation of amino acids by broken chloroplasts in the dark, supplemented with ATP and GTP, requires 9 mm Mg2+ for maximum activity. A requirement for monovalent cations is best filled by K+ (approx 30 mm) in the case of the light-driven, intact chloroplast system whereas, in the ATP-driven, broken chloroplast system, NH4+ (approx 80 mm) gave the highest activity. Autoradiographs of Na dodecyl sulfate-polyacrylamide gels of the products from both the light-driven, intact chloroplasts and from the ATP-driven, broken chloroplasts reveal qualitatively similar patterns. There are at least four radioactive polypeptides in the soluble protein fraction the dominant product being coincident with the large subunit of Fraction 1 protein. In the membrane fraction at least nine discrete products can be resolved.