MALIC DEHYDROGENASE ACTIVITY AT 101 C UNDER HYDROSTATIC PRESSURE

MORITA, RICHARD Y. (University of Nebraska, Lincoln) AND ROGER D. HAIGHT. Malic dehydrogenase activitv at 101 C under hydrostatic pressure. J. Bacteriol. 83:1341-1346. 1962.-No malic dehydrogenase activity was found to occur at 101 C at various hydrostatic pressures from 1 to 700 atm. However, activity was demonstrated with hydrostatic pressures above 700 atm, with optimal activity at 1,300 atm at the same temperature. Explanation of the data is based upon thermal denaturation of the enzyme, which involves a molecular volume increase of the enzyme. The molecular volume increase is counteracted by hydrostatic pressure. Pressures above 700 atm to 1,500 atm (highest employed) were sufficient to offset the denaturation by 101 C which probably resulted in an incomplete denaturation of malic dehydrogenase

INTERACTION BETWEEN THE PARAMETERS OF HYDROSTATIC PRESSURE AND TEMPERATURE ON ASPARTASE OF \u3ci\u3eEscherichia coli\u3c/i\u3e

HAIGHT, ROGER D. (University of Nebraska, Lincoln) AND RICHARD Y. MORITA. Interaction between the parameters of hydrostatic pressure and temperature on aspartase of Escherichia coli. J. Bacteriol. 83:112-120. 1962.-The data obtained from studies of an aspartase preparation and aspartase in cells of Escherichia coli indicate that there is an interaction between the parameters of hydrostatic pressure and temperature. Pressure was found to decrease aspartase activity at 45 C and lower in vitro and below 53 C in vivo, thereby indicating that when the enzymesubstrate complex is formed there is an increase in molecular volume which is counteracted by pressure. Above 53 C in vivo and above 45 C in vitro, temperature probably starts the unfolding process ot the enzyme to expose more reactive sites, while pressure then pushes the enzyme and substrate into closer proximity writh each other. Thus, pressure stimulated activity and also prevents further unfolding of the enzyme. Since the enzyme preparation retains about the same level of activity after being subjected first to 1000 atm at 56 C, the aspartase probably refolds into its original configuration or one similar to it, when subjected to 1 atm at 37 C. In all cases, the presence of the substrate was found necessary to protect aspartase from thermal inactivation or denaturation