Thermolability of Malic Dehydrogenase from the Obligate Psychrophile Vibrio marinus

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Abstract
Langridge, Patricia (Oregon State University, Corvallis), and Richard Y. Morita . Thermolability of malic dehydrogenase from the obligate psychrophile Vibrio marinus . J. Bacteriol. 92: 418–423. 1966.—The thermolability of malic dehydrogenase in whole cells of Vibrio marinus MP-1 grown at 15 C was compared with that of cell-free extracts and partially purified fractions. The intracellular enzyme was found to be stable between 0 C, and the organism's optimal growth temperature, 15 C. In cell-free extracts, considerable lability was noted even at 0 C, and this lability did not increase further until the enzyme was exposed to temperatures above the organism's maximal growth temperature (20 C). Twenty-fold purified enzyme was stable between 15 and 20 C, but both above and below this there was considerable inactivation. A 5-min exposure of both cold- and heat-inactivated enzyme to 15 C allowed reactivation, although to a different extent. Ammonium sulfate was found both to stimulate enzyme activity and to reactivate temperature-inactivated enzyme.