Occurrence of two different forms of protocatechuate 3,4-dioxygenase in a Moraxella sp

Two alternative forms of protocatechuate 3,4-dioxygenase (PCase) have been purified from Moraxella sp. strain GU2, a bacterium that is able to grow on guaiacol or various other phenolic compounds as the sole source of carbon and energy. One of these forms (PCase-P) was induced by protocatechuate and had an apparent molecular weight of 220,000. The second form (PCase-G) was induced by guaiacol or other phenolic compounds, such as 2-ethoxyphenol or 4-hydroxybenzoate. It appeared to be smaller (Mr 158,000), and its turnover number was about double that of the former enzyme. Both dioxygenases had similar properties and were built from the association of equal amounts of nonidentical subunits, alpha and beta, which were estimated to have molecular weights of 29,500 and 25,500, respectively. The (alpha beta)3 and (alpha beta)4 structures were suggested for PCases G and P, respectively. On the basis of two-dimensional gel electrophoresis, the alpha and beta polypeptides of PCase-G differed from those of PCase-P. Amino acid analysis supported this conclusion. Both PCases, however, had several other properties in common. It is proposed that both isoenzymes were generated from different sets of alpha and beta subunits, and the significance of these data is discussed.