Occurrence of Pseudovitamin B_<12> and Its Possible Function as the Cofactor of Cobalamin-Dependent Methionine Synthase in a Cyanobacterium Synechocystis sp. PCC6803

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To clarify the physiological function of pseudovitamin B12 in cyanobacteria, we determined pseudovitamin B12 contents and cobalamin-dependent methionine synthase activity in Synechocystis sp. PCC6803 grown under CoSO4-sufficient and -limited conditions. Pseudovitamin B12 and cobalamin-dependent methionine synthase activity (0.8 nmol/min/mg protein) were found in a homogenate of the Synechocystis cells grown for 10 d in the CoSO4-sufficient medium. The cellular pseudovitamin B12 contents increased significantly at the early logarithmic growth phase and thereafter decreased rapidly at the stationary phase; a similar fluctuation pattern was shown in the cobalamin-dependent methionine synthase activity. Although the CoSO4-limited conditions did not reduce the cell growth, pseudovitamin B12 contents and methionine synthase activity decreased significantly in the limited cells relative to the sufficient cells. These results indicate that the cyanobacterium Synechocystis sp. PCC6803 can synthesize pseudovitamin B12 de novo and utilize it as the cofactor for cobalamin-dependent methionine synthase.
財団法人学会誌刊行センターの論文
2009-12-01