Uptake and metabolism of folate by a folate-utilizing mutant of Pediococcus cerevisiae (8081-S) and the parent strain (8081).

Pediococcus cerevisiae 8081, which uses folinic acid for growth, and its nutritional mutant 8081/S, which utilizes folate, were compared with respect to their ability to take up and metabolize folate. In contrast to the parent strain 8081, which takes up very little folate, the uptake of folate by the mutant is a concentrative, saturable, and energydependent process. At low extracellular concentration (0.22 PM), folate which enters the cells is immediately metabolized, its uptake being rate limiting. Polyglutamates of reduced folate derivatives of unknown composition accumulate in the cells. At high extracellular concentration (80.8 PM), unaltered folate accumulates inside the cells and is slowly metabolized, mainly to NS,N’O-methylenetetrahydrofolate. Folinic acid and amethopterin inhibit the uptake of folate, suggesting that all three compounds may be taken up by the same mechanism. An unknown substance which seemed to be responsible for cessation of folate uptake by 8081/S cells after about 30 min of incubation was formed and excreted into the medium by both 8081 and 8081 /S.