© 1971 by The Society for Integrative and Comparative Biology
Pressure Effects on Catalysis and Control of Catalysis by Liver Fructose Diphosphatase from an Off-Shore Benthic Fish
Department of Zoology, University of British Columbia Vancouver 8, B. C, Canada
Institute of Arctic Biology, University of Alaska Alaska, Fairbanks, Alaska 99701
Institulo de Bioquimica, Universidad Austral de Chile Chile, Valdivia, Chile
SYNOPSIS: At low temperature (2°C), in the absence of FDP and Mg2+, the enzyme fructose disphosphatase (FDPase), extracted from the liver of an off-shore benthic Coryphaenoides species, is inactivated by exposures to relatively low pressures. The substrate, FDP, and the cofactor, Mg2+, protect against this inactivation, so that catalysis per se is not retarded by pressure. In contrast, at alkaline pH, pressure dramatically accelerates the catalytic rate when FDP and Mg2+ are saturating. The volume change of activation, 
V*, for Coryphaenoides FDPase under these conditions is about –40 cm3/mole. At low concentrations of FDP and saturating concentrations of cofactor, the reaction rate at alkaline pH is pressure-independent. Similarly, at low concentrations of Mg2+ but saturating concentration of FDP, the reaction rate is pressure-independent. The Km for FDP does not change measureably with pressure, while the Ka for Mg2+ increases slightly with pressure. Under conditions of low (probable physiological) FDP and Mg2+ concentrations, it is evident that the reaction rate is determined by the kinetic characteristics of the enzyme and not by its energy-volume relationships, a situation which would appear to be of functional and selective significance to an organism living under constantly high hydrostatic pressure. AMP is a potent specific inhibitor of Coryphaenoides FDPase. The K4 for AMP is essentially pressure-independent both at neutral and alkaline pH, suggesting that efficiency of AMP control of this enzyme is comparable at all pressures likely to be encountered in nature.