Figure 2.

Folate biosynthesis and regulation in plants. Black arrows indicate biosynthetic steps, red arrows and blunt-end arrows show activation and inhibition, respectively, of enzymatic steps by folate precursors. Precursors: GTP, guanosine triphosphate; DHN-P₃, dihydroneopterin triphosphate; DHN-P, dihydroneopterin monophosphate; DHN, dihydroneopterin; HMDHP, 6-hydroxymethyldihydropterin; HMDHP-P₂, 6-hydroxymethyldihydropterin pyrophosphate; DHP, dihydropteroate; DHF, dihydrofolate; THF, tetrahydrofolate; THF-Glu_(n), tetrahydrofolate polyglutamate; ADC, aminodeoxychorismate; pABA, para-aminobenzoic acid. Enzymes: GTPCHI, GTP cyclohydrolase I; DHN-P₃-diphosphatase, dihydroneopterin triphosphate pyrophosphatase; DHNA, dihydroneopterine aldolase; HPPK, HMDHP pyrophosphokinase; DHPS, dihydropteroate synthase; DHFR, dihydrofolate reductase; FPGS, folylpolyglutamate synthetase; ADCS, aminodeoxychorismate synthase; ADCL, aminodeoxychorismate lyase; GGH, gamma-glutamyl hydrolase.