The biosynthesis of porphyrins from porphobilinogen by Rhodopseudomonas spheroides. 2. The partial purification and some properties of porphobilinogen deaminase and uroporphyrinogen decarboxylase

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Abstract
Porphobilinogen deaminase and uroporphyrinogen decarboxylase were separated from cell-free extracts of R. spheroides by fractionation with ammonium sulphate. A reproducible "indirect" assay for uroporphyrinogen decarboxylase was devised with porphobilinogen as substrate with an excess of porphobilinogen deaminase. The Michaelis constant, temperature optimum and pH optimum of the partially purified porphobilinogen deaminase were determined. The Michaelis constant with porphobilinogen as substrate is unchanged in the presence of porphobilinogen a-carboxylic acid. Uroporphyrinogen decarboxylase acts on all 4 position-isomers of uroporphyrinogen and is unstable in the absence of sulphydryl compounds. R. spheroides, chick blood, yeast, and pig liver contain a heat-stable factor which stimulates coproporphyrin formation from porphobilinogen.