Slow, fast- and medium fast responses of ectotherms to temperature changes; a new mechanism of metabolic compensation in Helix pomatia ?

1.(1)|The maximum rates of PK and LDH from the foot of the snail Helix pomatia, measured at 20°C, are inversely proportional to the average temperature of the day on which the animal was collected and killed.2.(2)|If Vmax is calculated for the temperature established as the average temperature of the day on which the animal was collected and killed, PK activity turns out to be perfectly temperature-compensated, whereas LDH-activity increases slightly with temperature.3.(3)|The PK of the foot of the snail is inhibited by phospho-arginine (PArg) in a manner which suggests a phosphorylation/dephosphorylation mechanism. The degree of inhibition after an incubation time of 12–15 min depends on the concentration of PArg as well as on individual features of the pyruvate kinase preparation which cannot yet be resolved.4.(4)|The interaction of PArg with PK could provide a mechanism by which the rate of flow of PEP through this glycolytic branchpoint is controlled by temperature and by the locomotory activity of the animal. The time constant of this control mechanism would appear to lie between many minutes and a few hours.