|Title||Studies on Vitamin B12 Metabolism in HeLa Cells|
|Publication Type||Journal Article|
|Year of Publication||1971|
|Authors||Kerwar, SS, Spears, C, McAuslan, B, Weissbach, H|
|Journal||Arch Biochem Biophys|
In the present report some aspects of vitamin B12 metabolism in HeLa cells and other tissue culture lines have been investigated. Mangum et al. (1) previously reported the presence of higher levels of N5-methyl-H4-folate-homocysteine transmethylase in tissue culture cells grown in the presence of vitamin B12. The present experiments indicate that under the growth conditions used, HeLa cells do not contain sufficient vitamin B12 to satisfy the cobamide requirement of the transmethylase, and the increase in enzymatic activity that is observed when the cells are grown in the presence of vitamin B12 results from the conversion of the apoenzyme form of the enzyme to active holoenzyme. No effect of the vitamin on the oxidation of propionate to CO2 was observed in these cells suggesting that the amount of 5′-deoxyadenosyl B12(DBCC) present was sufficient so that the methylmalonyl CoA isomerase reaction was not rate limiting. Extracts of HeLa cells readily convert hydroxy-B12 to DBCC in the presence of ATP and a reducing system. The optimum conditions for the enzymatic synthesis of DBCC are described.