Stereochemistry and mechanism of the conversion of 5-aminolaevulinic acid into porphobilinogen catalysed by porphobilinogen synthase.

(3R)- and (3S)-Deuteriated forms of 5-aminolaevulinic acid have been synthesized and the (3R)-form shows a significantly larger isotope effect when incubated with porphobilinogen synthase from bovine liver and from Bacillus subtilis; based on this and on available crystal structures, a modified mechanism for the enzymic reaction is proposed.