期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1973
卷号：70
期号：9
页码：2585-2589
DOI：10.1073/pnas.70.9.2585
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Rapid growth of BHK cells in methioninedeficient medium required supplementation with homocysteine, B12, and over 40-fold greater levels of folic acid than growth in methionine-supplemented medium. The activity of the B12-dependent 5-methyltetrahydrofolate: homocysteine methyltransferase was studied in extracts of BHK cells grown in media containing various concentrations of the compounds of the enzyme reaction. The methyltransferase activity increased over 4-fold when B12-deficient deficient medium was supplemented with optimal levels of B12; this increase was not prevented by puromycin. Addition of homocysteine to growth medium containing methionine, B12, and folic acid was without effect. However, methyltransferase activity increased 2.5- to 4.0-fold further beyond the highest levels obtained in the presence of methionine, B12, and folic acid when homocysteine was substituted for methionine in the growth medium. This increase was blocked by puromycin and was not due to removal of feedback inhibition of activity by the product methionine. These results suggest that methyltransferase activity may be regulated in part by derepression of the enzyme's synthesis on substitution of the substrate homocysteine for the product methionine.
