Wild‐Type and Mutant Forms of Homoisocitric Dehydrogenase in the Yeast Saccharomycopsis lipolytica
Abstract
Homoisocitric dehydrogenase (EC 1.1.1.155) has been purified 525‐fold from the yeast Saccharomycopsis lipolytica with a yield of 25%. The preparation was judged to be homogeneous by electrophoresis under denaturing and non‐denaturing conditions and by isoelectric focusing; it consisted of a single protein with molecular weight of 48000. In the presence of homoisocitric acid, a higher molecular weight was observed, suggesting a dimeric structure for the native enzyme.
Complementing mutants devoid of homoisocitric dehydrogenase activity mapped at two closely linked loci (lys9 and lys10). Lvs10 mutants displayed NAD‐reducing activity, whereas lys9 mutants retained some carboxylating activity.
Our results are best explained by the assumption that the active enzyme is a dimer of identical subunits involved in successive dehydrogenation and decarboxylation steps.
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