Analysis of the relationship between the extrinsic 30-kDa protein, manganese and oxygen evolution in the thylakoid of Chlamydomonas reinhardtii grown under manganese-deficient conditions

Abstract

The content and stability of an extrinsic protein in the thylakoid of a green alga Chlamydomonas reinhardtii which has a relative molecular weight of 30 000 and corresponds to the ‘33-kDa’ protein involved in oxygen evolution in spinach chloroplast were studied with the cells grown in a manganese-deficient medium. The amount of the 30-kDa protein in the thylakoid did not change even when the content of manganese in the membrane was decreased significantly and the activity of oxygen evolution was reduced concomitantly under manganese-depleted conditions. The stability of the 30-kDa protein in the membrane, which was determined by the susceptibility of the protein to the treatment with an alkaline buffer and sonication, also showed no significant change between the cells grown with and without manganese. The thylakoid membrane of the cells grown under manganese-deficient conditions was devoid of the loosely bound manganese atoms located at the hydrophilic environment of the membrane probably at the interface between the 30-kDa protein and the reaction center complex of Photosystem II, judging from the partitioning behavior of manganese atoms on butanol/water phase partitioning of the thylakoid. These results suggest that the manganese atoms involved in oxygen evolution are not required for the binding of the 30-kDa protein to the Photosystem II membrane.