Thermolability of Malic Dehydrogenase from the Obligate Psychrophile Vibrio marinus.

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.