“Also vitamin B12 is known to decrease the PABA requirement for a PABA auxotroph of E. coli (Davis, 1951; Gots and Chu, 1952).”
“ Vitamin B12 has been reported (Shive, 1950) to potentiate PABA action as, in its presence, higher concentrations of SA are required to inhibit the biosynthesis of methionine, xanthine and serine.”