Temperature-dependent enzyme kinetics during avian ontogeny: malate dehydrogenase in the common crow (Corvus brachyrhynchos) and the pintail (Anas acuta)

Abstract

The electrophoretic patterns and temperature-dependent kinetics of cytoplasmic malate dehydrogenase from liver of juvenile and adult representatives of the common crow (Corvus brachyrhynchos), an altricial species, and the pintail (Anus acuta), a precocial species, were examined. Starch gel electrophoresis revealed two major isoenzymes in each case. The isoenzymes of the juvenile and adult crow exhibit different electrophoretic mobilities, while those of the juvenile and adult pintail exhibit identical mobilities. Assay temperature has no statistically significant age-specific or species-specific effects on several kinetic properties of malate dehydrogenase. In all cases, the Michaelis constant (K_m) of oxaloacetate for malate dehydrogenase remains fairly stable below 15 °C, but increases three- to four-fold from 15 ° to 45 °C. Values of activation energy vary between 12.1 and 15.0 kcal/mol. Q₁₀ values for reaction velocities at minimum K_m substrate levels are about 1.0 between 30° and 40 °C. The adaptive significance of the observed effects is discussed in relation to poikilothermic stages of the early posthatching ontogeny of birds.