Purification and chemical modifications of porphobilinogen oxygenase

Abstract

Porphobilinogen oxygenase from wheat germ was purified and was found to be a cationic protein containing 8 mol of nonheme iron and 8–10 mol of labile sulfide per mole of enzyme ( M r, 100,000). The enzyme isolated from either wheat germ or rat liver microsomes was found to exist in multiple molecular weight forms. When succinylated, only one molecular weight form of 25,000 was obtained and it retained full activity. It had lost all of the sigmoidal kinetics characteristic of the native enzyme. While the native enzyme had an n = 3.5, the succinylated enzyme showed Michaelian kinetics. A K m of approximately 1.70 m m was determined for the succinylated wheat germ enzyme, and a K m of approximately 2.5 m m was found for the succinylated microsomal enzyme. Acetylation of the enzyme afforded an active acetylated enzyme which showed allosteric kinetics and multiple molecular weight forms. The products formed by the succinylated enzyme were the same as those formed by the native enzyme.