© 1971 by The Society for Integrative and Comparative Biology
Effects of Pressure and Temperature on the Catalytic and Regulatory Properties of Muscle Pyruvate Kinase from an Off-Shore Benthic Fish
Department of Zoology, University of British Columbia Vancouver 8, B. C, Canada
SYNOPSIS. Muscle pyruvate kinase from an abyssal Coryphaenoides species occurs as a single electrophoretic form with an isoelectric point of about pH 6.0. Maximum catalytic rates are dramatically reduced by pressure. For catalysis at 3°C, the volume change of activation, 
V*, is about 44 cm3/mole (calculated between 14.7 and 8000 psi). The value ot V* decreases at higher temperatures but is pH independent. The activation energy for rattail muscle pyruvate kinase at 14.7 psi is about 13 Kcal/mole and doubles at 12,000 psi. Mg2+ saturation kinetics involve positive site-site interactions. Hill plots yield n values of about 2.4 and Ka values of about 2 mM (at 3°C), and these constants are pressure independent. 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 constant lor PEP is not affected by pressure, but the apparent Km increases somewhat with pressure. FDP dramatically activates rattail muscle pyruvate kinase (500% activation with 0.1 mM FDP) by (1) reducing the KmPEP, (2) increasing the maximum velocity, and (3) overriding negative ATP modulation of the enzyme. The latter control feature is strictly dependent upon pressure and is not observed at low pressure. In the presence of FDP, the Km for PEP decreases at high pressures, in this way counteracting the inhibitory effects of pressure. Under low concentrations of substrates, pyruvate kinase activity is probably determined by its kinetic properties and not by energy-volume relationships.