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：1982
卷号：79
期号：14
页码：4248-4251
DOI：10.1073/pnas.79.14.4248
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Methionine (Met) dependence--i.e., the inability of cultured cells to grow when Met is replaced by its immediate precursor homocysteine (Met-Hcy+ medium)--is a frequent component of the oncogenically transformed phenotype. Normal cells, on the other hand, grow in this medium. There have been reports [Hoffman, R. M. & Erbe, R. W. (1976) Proc. Natl. Acad. Sci. USA 73, 1523-1527; Hoffman, R. M., Jacobsen, S. J. & Erbe, R. W. (1978) Biochem. Biophys. Res. Commun. 82, 228-234] of normal or higher rats of Met biosynthesis in Met-dependent cells and a postulation that Met-dependent cells are deficient in utilization of endogenously synthesized Met as opposed to exogenously supplied Met. To answer the critical question of what biochemical reaction(s) requires preformed Met in Met-dependent cels, we labeled cells with Met-free [35S]Hcy or [35S]Met and determined the levels of Met, S-adenosylmethionine (AdoMet), and S-adenosylhomocysteine (AdoHcy). We report here experiments that demonstrate that Met-dependent cells synthesize a normal amount of endogenously synthesized Met and are deficient in utilizing this Met for AdoMet synthesis. In contrast, exogenously supplied Met is utilized normally for AdoMet biosynthesis. The ratio of AdoMet to AdoHcy is low in Met-dependent cells growing in Met-Hcy+ medium but is normal in Met+Hcy- medium. We determined that the low AdoMet/AdoHcy ratio probably limits growth of Met-dependent cells in Met-Hcy+ medium.
