Fig 2
From: Bacteria increase host micronutrient availability: mechanisms revealed by studies in C. elegans
Structure of tetrahydrofolate (THF). THFs are composed of pterin, PABA, and glutamate. The pterin moiety is substituted at N5 (R1) and/or N10 (R2) nitrogen atoms with either a methyl (-CH3), formyl (-CH=O) methylene (=CH2), or methenyl (-CH4) group. THFs also vary in the length of their glutamate “tail,” which varies depending on function