Abstract
δ-Aminolevulinic acid (ALA) dehydratase has been purified 160-fold from Spirillum itersonii by a combination of ammonium sulfate fractionation and chromatography on calcium phosphate gel and Sephadex G-200. The enzyme requires magnesium or manganese ions for activity as well as a sulfhydryl agent. The K m for δ-aminolevulinic acid is 0.1 m m. Levulinic acid is a competitive inhibitor of the enzyme, with a K i of 1.8 m m. Hemin (0.1 m m) and protoporphyrin (0.2 m m) are only slightly inhibitory. The specific activity of ALA dehydratase in crude cell extracts is less than that of ALA synthetase, and the level of dehydratase activity is similar in cells grown under high and low aeration. Growing cultures of the organism do not accumulate ALA or porphyrins but accumulation of ALA occurs upon addition of levulinic acid. It is concluded that ALA synthetase has a major role in regulating tetrapyrrole synthesis in S. itersonii despite the relatively low activity of the dehydratase.
Published Version
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