Transport and metabolism of folates by bacteria.

Transport of labeled folic acid (PteGlu), pteroylpolyglutamates (PteGlu,.,),5-methyl-tetrahydrofolate (5.methyl-HPteGlu), and methotrexate in late-log phase cells of Lacfobacillus casei was active, and subject to inhibition by unlabeled pteroyhnonoglutamates, pteroylpolyglutamates, and iodoacetate, but not glutamate or glutamate dipeptides.Pteroylpolyglutamates were transported without prior hydrolysis and shared a common uptake system with pteroylmonoglutamates.The afIinity and maximum velocity of PteGlu, uptake decreased with increasing glutamate chain length (K,: PteGlul, 0.03 PM; PteGlus, 0.32 PM; PteGlur, 1.9 pM; PteGlus, 3.7 PM) and comparisons with growth response curves suggested that polyglutamates were more effectively utilized by Z. casei, once transported, than monoglutamate.No concentration of 5-methyl-HPteGlus.sinside the cells was observed.The major folate metabolites found in L. casei preloaded with high levels of [3H]PteGlu (0.5 pM) were IO-formyl-HsteGluz and IO-formyl-PteGlu.Both compounds were released, the monoglutamate more rapidly.Pteroyltriglutamate formation appeared to be a rate-limiting step in intracellular metabolism.No IO-formyl-PteGlu was found in iodoacetate-treated cells and efflux was inhibited.Cells preloaded with low levels of [3H]PteGlu (7 m) metabolized the vitamin to polyglutamate forms, the major derivatives being HPteGlu,.First order exit rates of labeled folate from preloaded L. cosei indicated an inhibition of PteGlu uptake with time.Exit rates dropped from 0.05 mm1 to <0.002 min+ as intracellular folate was metabolized from monoglutamate to polyglutamate derivatives (n 2 3).In the latter case, materials lost by efflux were breakdown products and no folate of glutamate chain length greater than two was released.Pediococcus cerevisiae actively transported 5.methyl-HPteGlu but did not take up 5-methyl-H4PteGlu3.8.No active accumulation of 5-methyl-HcPteGlu was observed in Streptococcus fuecalis.Since the discovery of pteroylheptaglutamates in yeast (2), many authors have reported the existence of pteroylpolygluta-