Glycolytic Enzyme Binding and Metabolic Control in Estivation and Anoxia in the Land Snail Otala Lactea

Abstract

The mechanisms controlling glycolytic rate were examined in foot muscle of the terrestrial snail Otala lactea (Miiller) (Pulmonata, Helicidae), during short and long periods of estivation and anoxia. Binding associations between glycolytic enzymes and the particulate fraction of the cell were assessed in both states. The percentage of enzyme activity bound to particulate matter decreased significantly over the short term (4 days estivation and 14.5 h anoxia); significant changes were seen for hexokinase (HK), phosphofructokinase (PFK), aldolase and lactate dehydrogenase (LDH) in estivation and, for these enzymes plus triosephosphate isomerase and pyruvate kinase (PK), in anoxia. Over the longer term in estivation (22 days) and anoxia (45 h), enzyme binding returned to control values. Tissue content of fructose-2,6-bisphosphate, a potent phosphofructokinase activator, decreased under all experimental conditions. Total glycogen phosphorylase activity decreased during short-term anoxia (14.5 h) and during long-term estivation (22 days), but the percentage of the active a form decreased significantly during anoxia only. Significant changes in the maximal activities of several enzymes were observed during both estivation and anoxia. Decreases inthe maximal activity of HK, PFK, glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase (PGK) and LDH were observed during long-term estivation. Increases in PGK and PK maximal activity in short-term anoxia and aldolase and PGK in long-term anoxia were also observed. These results suggest that changes in glycolytic enzyme binding may be part of an immediate mechanism used to cause a rapid decrease in glycolytic flux and initiate glycolytic rate depression, which also includes a reduction of fructose-2,6-bisphosphate content and decreased glycogen phosphorylase activity. In the long term, however, control of snail glycolytic rate is reorganized, so that enzyme binding associations revert to the control values. In the long term, then, control is mediated by lower fructose- 2,6-bisphosphate concentrations and, during estivation, also by a decrease in maximal enzyme activities.