The polyglutamate nature of plant folates

Abstract

Folylpolyglutamates were extracted from a variety of higher plant tissues and cleaved to p-aminobenzoyl polyglutamates by acid-base and ZN-HCl treatments. After purification as azo dyes and reconversion to p-aminobenzoylpolyglutamates these derivatives were separated according to their glutamyl chain lengths by HPLC on Partisil SAX. Polyglutamate concentrations were calculated by reference to standard calibration curves. Tomato leaf extracts contained relatively high folate contents (7.55 nmol/g fr. wt) and these were mainly hexa- (23%) and heptaglutamates (30%). Carrot root extracts had low folate contents (0.22 nmol/g fr. wt) with diglutamates accounting for 69% of the folate recovered after chromatography. Carboxypeptidase treatments of broccoli floret extracts indicated that the folylpolyglutamates principally contained γ-glutamyl linkages. [ 3H]Glutamate and [ 14C] p-aminobenzoate were incorporated into the polyglutamates of broccoli seedlings but equilibrium of the label with the endogenous pools was not attained after a 48 hr pulse feeding. Difrerential, oxidative cleavage of broccoli leaf folates into three polyglutamate pools showed that the formyl- and methylfolates were mainly (80%) diglutamyl derivatives. The methylene and unsubstituted folates of this tissue were principally (78%) hexaglutamates.