Folate metabolism in mammalian cells in culture. I Partial characterization of the folate derivatives present in L1210 mouse leukemia cells.

Chromatographic procedures were developed which permit the separation of the monoglutamylfolic acid derivatives from each other and from their polyglutamyl congeners. Using these methods, the cellular folate derivatives in logarithmically growing L1210 cells were found to consist entirely of polyglutamyl derivatives. When ascorbate extracts of these cells were digested with hog kidney gamma-glutamylcarboxypeptidase and then chromatographed on DEAE-cellulose columns, the cellular folates eluted coincident with tetrahydrofolate, 5-formyltetrahydrofolate, 10-formyltetrahydrofolate, and 5-methyltetrahydrofolate, with minimal amounts associated with folate (approximately 0.8%) or dihydrofolate (approximately 0.4%). When these experiments were repeated on cells previously depleted of folates which were then grown on 0.4 muM pteroylglutamic acid (a concentration insufficient to maintain an optimal growth rate) more than 95% of the folates were again found in polyglutamyl form. These results imply that the polyglutamyl derivatives found are not storage forms of enzymatically active cofactor, but rather are the actual cofactor forms used by these mammalian cells.