Temperature-dependent activation or inactivation of glycogen phosphorylase and synthase of fat body of the silkworm Philosamia cynthia: The possible mechanism of the temperature-dependent interconversion between glycogen and trehalose

Abstract

When diapausing pupae of the silkworm, Philosamia cynthia, were exposed to low temperature (2°C), fat body glycogen was converted into haemolymph trehalose, whereas the reverse reaction took place when the pupae were returned to a higher temperature (20–25°C). Concomitant with the above interconversion between glycogen and trehalose, the following changes were observed for glycogen phosphorylase and synthase of fat body. (1) Fat body glycogen phosphorylase b was converted to the a form when the pupae were exposed to low temperature whereas the reverse conversion occurred when exposed to the higher temperature. (2) Fat body glycogen synthase b was transformed to the a form when the pupae were transferred from 2°C to 25°C and the active form then decreased gradually. If the pupae were returned from 25°C to 2°C, the synthase activity remained at a low level. (3) Total phosphorylase activity remained constant, irrespective of the change in temperature, whereas total synthase activity increased when the pupae were exposed to a higher temperature. Based upon the above obserations, it is concluded that the two enzymes act as key enzymes regulating temperature-dependent interconversion between glycogen and trehalose in this insect.