Pergamon Comp.Biochem. Physiol. Vol.107n,No. 4, pp. 585-591,1994 Copyright © 1994 Elsevier Science Ltd Printed in Great Britain.All rights reserved 0305-0491/94$6.00 + 0.00 Regulation of pyruvate kinase (PK) from the ventricle of the land snail Helix lucorum L. during early and prolonged estivation and hibernation Basile Michaelidis and Theologos Pardalidis Laboratory of Animal Physiology, Department of Zoology, Science School, University of Thessaloniki, GR-54006 Thessaloniki, Greece The kinetic properties of pyruvate kinase (PK) from the ventricles of early and prolonged estivated and hibernated land snails, Helix lucorum, were studied. The kinetic properties of PK from the ventricles of snails accfimated to cold for 4 days and 2 months were also determined. Short estivation (4 days) converted the PK to a less active form, possibly via enzyme phosphorylation. After 2 months of estivation, PK exhibited kinetic properties similar to control enzyme, except that the Vmx increased about 2-fold, indicating metabolic reorganization. During early and prolonged hibernation, the kinetic properties of PK did not change significantly. The results indicate that low temperature and low pH may be the main modulators of enzyme activity in the ventricle of H. iucorum during hibernation. Key words: Land snail; Estivation; Hibernation; Ventricle; Pyruvate kinase; Glycolysis; Regulation. Comp. Biochem. Physiol. I07B, 585-591, 1994. Introduction Land snails respond to unfavorable conditions (dehydration, low temperature, food depri- vation) by entering a state of quiescence (dormancy). In this state oxygen consumption is greatly reduced and metabolic rate drops below the standard resting state (Nopp, 1974). The dormant period is characterized by an increase in CO2 content in extracellular fluids, which results in a drop of extracellular and intracellular pH (pHi) (Barnhart and McMahon, 1988). It has been shown that hyper- capnia strongly depresses oxygen consumption in Otala lactea and it has been proposed that the fall of pHi as a result of hypercapnia may be involved in the depression of metabolic rate during estivation (Barnhart, 1989; Barnhart and McMahon, 1987; Rees and Hand, 1990). Regu- lation of glycolysis via intracellular pH has been considered elsewhere (Busa and Nuccitelli, 1984) and it is known that a drop in pH i results Correspondence to: B. Michaelidis, Laboratory of Animal Physiology, Department of Zoology, Science School, University of Thessaloniki, GR-54006 Thessaloniki, Greece, Fax: 206-138. Received 15 July 1993; accepted 22 September 1993. in the suppression of the glycolytic rate by inhibiting the key glycolytic enzyme, phospho- fructokinase (PFK). Specifically, a drop in pHi results in a shift of enzyme molecules to a dissociated form and consequently to loss of enzyme activity (Carpenter and Hand, 1986a; Somero and Hand, 1990). Recent studies, however, have shown that the depression of the glycolytic rate in the tissues of land snails during entry into estivation is inde- pendent of hypercapnia (Rees and Hand, 1991). More extensive studies have shown that mechanisms involving the covalent modification of PK and PFK, possibly via phosphorylation/ dephosphorylation of enzymes, the regulation of PFK via the potent activator fructose-2,6-bis- phosphate (F-2,6-P2) and the binding of glyco- lytic enzymes to subcellular particles, may be involved in metabolic rate depression in the tissues of land snails during dormancy (Storey and Storey, 1990). Another mechanism which may be involved in the depression of oxygen consumption in estivating snails is the low supply of oxygen to the tissues through circulation. During 585