YEAST PORPHOBILINOGEN DEAMINASE ALSO FORMS ENZYME-PYRROLE INTERMEDIATES

The enzyme porphobilinogen deaminase (PEG deaminase, EC 4.3.1.8) catal yzes the condensation of four molecules of PEG to give the linear tetr apyrrol, hydroxymethylbilane. It has been shown that this enzyme forms stable mono-, di-, tri- and tetrapyrrol-enzyme covalent complexes. Wh en the enzyme, partially purified in the absence or presence of phenyl methylsulfonyl fluoride (PMSF) and preincubated with PEG, was applied on DEAE-cellulose columns, three peaks with PEG deaminase activity wer e detected. Using Ehrlich's reagent, it was found that the active peak s corresponded to mono-, di- and tri-pyrrylmethane-enzyme complexes. T herefore, the mechanism of action of PBG deaminase from Saccharomyces cerevisiae also involves the sequential addition of four PEG units, le ading to the formation of the enzyme-substrate intermediate complexes, as has already been described for the same enzyme from other sources.