Homoisocitric dehydrogenase from yeast

Wild‐Type and Mutant Forms of Homoisocitric Dehydrogenase in the Yeast Saccharomycopsis lipolytica

“…This situation is very similar to that reported for other hysteretic enzymes [I41 like the NADP-isocitrate dehydrogenase [5] and reinforces the earlier proposal on the similarity of both dehydrogenases [3]. It has been proposed by Frieden [14] that this slow response of an enzyme to a rapid change in substrate concentration could be an important regulatory process for enzymes catalyzing reactions at branch points of a pathway.…”

“…In view of our results, it is also possible that leaky homoisocitric dehydrogenase mutants are those mutants which carry out oxidation but not decarboxylation (our lyslc) mutants). We have no direct evidence for oxaloglutaric acid being the product of such a partial reaction (see Table 3): should however such an intermediate be formed it could spontaneously yield 2-oxoadipic acid [3] giving rise to the leaky phenotype.…”

“…Standard conditions were: 1.5 mM potassium threo-( f)-homoisocitrate; 4.5 mM MgC12; 6 mM NAD in 0.1 M potassium phosphate buffer pH 8.5. No correction was made to account for the threo-(-) isomer being the actual substrate [3,9].…”

“…The reductive carboxylation of oxoadipic acid was estimated essentially according to [3]. The incubation mixture consisted of: 0.1 M potassium phosphate buffer pH 7.5; 4.5 mM MgCl2; 1 mM NaDH; 10 mM 2-oxoadipate.…”

“…An enzyme fraction, termed homoisocitric dehydrogenase was purified 500-fold by Rowley and Tucci [3] from Saccharornyces cerevisiae and shown to catalyze the oxidative decarboxylation of homoisocitric acid. No evidence could be found for the existence of oxaloglutaric acid, a postulated intermediate of the reaction.…”