Yeast porphobilinogen deaminase also forms enzyme-pyrrole intermediates

The enzyme porphobilinogen deaminase (PBG deaminase, EC 4.3.1.8) catalyzes the condensation of four molecules of PBG to give the linear tetrapyrrol, hydroxymethylbilane. It has been shown that this enzyme forms stable mono-, di-, tri- and tetrapyrrole-enzyme covalent complexes. When the enzyme, partially purified in the absence or presence of phenylmethylsulfonyl fluoride (PMSF) and preincubated with PBG, was applied on DEAE-cellulose columns, three peaks with PBG deaminase activity were detected. Using Ehrlich's reagent, it was found that the active peaks corresponded to mono-, di- and tri-pyrrylmethane-enzyme complexes. Therefore, the mechanism of action of PBG deaminase from Saccharomyces cerevisiae also involves the sequential addition of four PBG units, leading to the formation of the enzyme-substrate intermediate complexes, as has already been described for the same enzyme from other sources.