PROTEIN-PHOSPHORYLATION PATTERNS DURING ESTIVATION IN THE LAND SNAIL OTALA-LACTEA

Protein phosphorylation patterns were investigated in whole tissues and subcellular fractions of active and aestivating Otala lactea (Muller) (Pulmonata, Helicidae). Measurement of overall protein phosphorylation showed that incorporation of P-32 increased until the second day after injection and remained constant for the remaining 4 days of the time course. Comparison of tissues from aestivating and active snails on day 3 showed a decreased protein phosphorylation in aestivating snails (44% of active). No differences in total and protein-associated radioactivity for foot, mantle or haemolymph were observed. Subcellular fractionation of the hepatopancreas localized the changes to plasma membrane, microsomal, and cytosolic fractions: values for aestivating animals were reduced to 71, 37 and 58% of the corresponding active values. Separation of the individual subcellular fractions on isoelectric focusing columns revealed differences in the phosphate incorporation patterns. Plasma membrane from aestivating animal hepatopancreas had a lower overall level of incorporation and fewer radioactive peaks in the pH 7-10 region than did the plasma membrane fraction from active animals. SDS-PAGE analysis of plasma membrane fractions from active and aestivating snails showed a relative decrease in phosphorylation between 60-80 kDa and 30-40 kDa. IEF analysis of cytosolic proteins from aestivating snail hepatopancreas also showed peaks of radioactivity that were apparently shifted by 0.3 pH units toward higher pi values. Increased phosphate incorporation was observed at a peak that corresponded to the pi value for pyruvate kinase in aestivating snails but definite assignment of peaks was not possible. SDS-PAGE analysis of cytosolic proteins showed an aestivation-related decrease in relative protein phosphorylation between 30-35 kDa and 40-45 kDa. A relative increase in phosphorylation during aestivation was observed for proteins between 16-22 kDa. Overall, the data indicate that snails dramatically alter their protein phosphorylation pattern in hepatopancreas during aestivation.