Lithium dodecyl sulfate/polyacrylamide gel electrophoresis of thylakoid membranes at 4°C: Characterizations of two additional chlorophyll a-protein complexes

Abstract

Lithium dodecyl sulfate/polyacrylamide gel electrophoresis of Chlamydomonas reinhardtii thylakoid membranes at room temperature gave 2 chlorophyll-protein complexes. CP I and CP II, as reported previously. However, when the electrophoresis was performed at 4.degree. C, there was an increase in the amount of chlorophyll associated with CP I and CP II, and in addition, 3 other chlorophyll-protein complexes appeared. Two of these complexes, designated CP III and CP IV, were characterized and were similar in their compositions. Each complex contains 4-5 molecules of chlorophyll a, 1 molecule of .beta.-carotene, and 1 polypeptide chain. The apoprotein of CP III is polypeptide 5 (MW 50,000) and that of CP IV is polypeptide 6 (MW 47,000); the 2 polypeptides are structurally unrelated. Chlorophyll-protein complexes similar to C. reinhardtii CP III and CP IV were also detected in higher plants (e.g., Pisum sativum). The apoproteins of the higher plant complexes are immunochemically related to those of the C. reinhardtii complexes, as shown by crossed immunoelectrophoresis. Absorption spectra of CP III and CP IV at -196.degree. C revealed a component at 682 nm. This observation, together with the previous results on photosystem II mutants, provide indirect evidence that CP III and CP IV may be involved in the primary photochemistry of photosystem II.