Properties of Pyruvate Dehydrogenase from the Land Snail,Otala lactea:Control of Enzyme Activity during Estivation

Abstract

The kinetic properties and regulation of pyruvate dehydrogenase (PDH) activity during estivation and recovery were examined in foot muscle and hepatopancreas of the terrestrial snail, Otala lactea (Muller) (Pulmonata, Helicidae). During estivation, the percentage of PDH in the active a form (PDHa) decreased from a control value of 98% to an estivating value of approximately 60% in both foot and hepatopancreas but the time course for changes in PDHa activity was different for the two tissues. Foot PDHa steadily decreased from the initiation of estivation until 20 h; after this time, the levels of PDHa showed no further change. Hepatopancreas PDHa levels did not decrease until 20 h after the initiation of estivation, after which time they rapidly dropped to reach a new, constant, estivating level by 30 h. Recovery curves for both tissues showed that PDHa had reached control levels 1 h after the reintroduction offood and water. Kinetic parameters of PDHa were also examined. The Michaelis constant value (Km)for pyruvate was 274 μM (foot) or 164 μM (hepatopancreas) with a maximal activity of 0.195 IU/g wet weight for foot and 0.120 IU/g wet weight for hepatopancreas. The Hill coefficient for both enzymes was not significantly different from 1.0, which demonstrates that the dehydrogenase activity was not cooperative with respect to pyruvate. Michaelis constants for CoA were 6.4 μM and 20.4 μM for foot and bepatopancreas, respectively. Both enzymes showed maximal activity under alkaline conditions with pH optima occurring at 8 (foot) and 7.5 (hepatopancreas).