Two structurally different NADP-specific isocitrate dehydrogenases in an obligately psychrophilic bacterium, Vibrio sp. strain ABE-1.

Two isozymes of NADP-specific isocitrate dehydrogenase (EC 1.1.1.42) were purified from the obligately psychrophilic marine bacterium Vibrio sp, strain ABE-1. Isozyme I purified by Blue-Sepharose column chromatography (Mr=about 85kDa) was proved to consist of two subunits (Mr=ca. 42kDa) by sodium dodecyl sulfate polyacrylamide gel electrophoresis and cross-linking with dimethyl suberimidate. Isozyme II purified by NADP-Sepharose column chromatography was a single large polypeptide (Mr=ca. 85kDa). This extremely thermolabile isozyme was easily inactivated above 15° and reactivated by chilling at 0° in the presence of 2-mercaptoethanol. Even when inactivated completely at 40° it could be renatured to about 40% of the original activity under the appropriate conditions. Isozyme I once denatured could not be renatured.