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Effects of Pressure and Temperature on the Catalytic and Regulatory Properties of Muscle Pyruvate Kinase from an Off-Shore Benthic Fish
Authors:MUSTAFA  TARIQ; MOON  THOMAS W; HOCHACHKA  PETER W
Institution:Department of Zoology, University of British Columbia Vancouver 8, B. C, Canada
Abstract:SYNOPSIS. Muscle pyruvate kinase from an abyssal Coryphaenoidesspecies occurs as a single electrophoretic form with an isoelectricpoint of about pH 6.0. Maximum catalytic rates are dramaticallyreduced by pressure. For catalysis at 3°C, the volume changeof activation, {Delta}V*, is about 44 cm3/mole (calculated between14.7 and 8000 psi). The value ot {Delta}V* decreases at higher temperaturesbut is pH independent. The activation energy for rattail musclepyruvate kinase at 14.7 psi is about 13 Kcal/mole and doublesat 12,000 psi. Mg2+ saturation kinetics involve positive site-siteinteractions. Hill plots yield n values of about 2.4 and Kavalues of about 2 mM (at 3°C), and these constants are pressureindependent. The Km values for ADP increase slightly with pressure.PEP saturation curves are complex: at high PEP concentrations,the n values are about 2–2.5, while at low PEP levels,values for the Hill constant are about 1.0. The Hill constantlor PEP is not affected by pressure, but the apparent Km increasessomewhat with pressure. FDP dramatically activates rattail musclepyruvate kinase (500% activation with 0.1 mM FDP) by (1) reducingthe KmPEP, (2) increasing the maximum velocity, and (3) overridingnegative ATP modulation of the enzyme. The latter control featureis strictly dependent upon pressure and is not observed at lowpressure. In the presence of FDP, the Km for PEP decreases athigh pressures, in this way counteracting the inhibitory effectsof pressure. Under low concentrations of substrates, pyruvatekinase activity is probably determined by its kinetic propertiesand not by energy-volume relationships.
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