Abstract
A new enzyme, 2-methylisocitrate dehydratase, isolated from Yarrowia lipolytica, functioning in the methylcitric acid cycle for propionate metabolism, had a pI of 4.4 and a M r of 69,500. The enzyme was composed of 624 residues of amino acids per molecule. No cofactor was required for full enzyme activity. The enzyme was competitively inhibited by three-D s -isocitrate (K i =68 mM), but not by any other tested metabolites. The enzyme was weakly inhibited by some thiol reagents, but not by any metal-chelating reagents, differing from aconitase, which dehydrates 2-methylisocitrate. This difference between the enzymes made it possible to estimate the activity of the new enzyme even in crude cell-free extracts. The enzyme was constitutively synthesized, but had no regulatory function in the methylcitric acid cycle. The enzyme was supposed to have evolutionarily developed from a hypothetical and prototypical isocitrate dehydratase.
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