Folate oligoglutamate:amino acid transpeptidase

A new and previously unrecognized enzyme activity folate oligoglutamate:amino acid transpeptidase (folate transpeptidase), was detected in rat liver extracts. This activity involves the exchange of the terminal gamma-glutamyl residue (where PteGlu represents pteroylglutamic acid) of H4PteGlu-gamma-Glu, PteGlu-gamma-Glu, or p-aminobenzoyl-Glu-gamma-Glu for an amino acid such as [14C]glutamic acid, [14C]methionine, [14C]glutamine, or [14C]glycine. In the case of substrates PteGlu2 and [14C]Glu, the product is PteGlu-gamma-[14C]Glu. The enzyme responsible for catalyzing this activity was purified 39,000-fold by precipitation of inactive protein, fractionation on anionic and molecular sieve columns, and chromatography on diaminohexane-Sepharose. The enzyme functions maximally at pH 7.9, shows an absolute requirement for sulfhydryl reductants, and appears to have a molecular weight of 65,000. The function of folate transpeptidase is not known. A second, though much weaker, enzyme activity, tetrahydrofolic acid:amino acid ligase (folate ligase), co-purified with folate transpeptidase through all steps. Folate transpeptidase and the associated folate ligase activity were separated from folate polyglutamate synthetase during the initial steps of the purification procedure.