Inhibition of Porphobilinogen Synthase Activity by 4,5-Dioxovalerate

The effect of 4,5-dioxovaleric acid on the activity of porphobilinogen(PBG) synthase (formerly 5-aminolevulinic acid dehydratase,EC 4.2.1.24[EC]) of the porphyrin synthetic pathway was studiedwith the enzyme purified from Chlorella regularis. 4,5-Dioxovalericacid, a metabolite of 5-aminolevulinic acid, competitively inhibitedPBG synthase with a K_i value of 1.4 mM. The concentration forthe half inhibition of 4,5-dioxovaleric acid (7 mM) was slightlylower than that for the known competitive inhibitor, levulinicacid (12 mM). (Received October 8, 1984; Accepted December 13, 1984)