The Enzymes of Glycogen and Trehalose Synthesis in Silk Moth Fat Body.

Since the demonstration of trehalose as the major blood sugar of insects (I), considerable attention has been given to the metabolism and functions of this disaccharide, and some outline of its physiological role is beginning to emerge. In some species, trehalose has been shown to serve as a mobile energy source for flight, and its levels in the blood have been implicated in the control of the expenditure of flight energy (2). But high levels of trehalose are also present in the blood of nonflying stages and of species which apparently use lipid for flight energy (3). In silkworm larvae, trehalose has been suggested as a source of carbon for chitin synthesis during molting (4). The levels of blood trehalose vary greatly in the developmental history of different species, and, in all probability, trehalose has been adapted to diverse functions within the class Insecta. Whatever its role, blood trehalose seems to be subject to quantitative regulation. Several species of lepidoptera are capable of homeostatic control of the levels of trehalose in the blood (5, 6). Indeed, the generality of such regulation is suggested by the constant and characteristic level of this sugar within the blood of each developmental stage of each species (3). This homeostasis could be the result of the controlled degradation of trehalose, and, in this connection, an inhibitor of the enzyme trehalase has been found in blowfly blood (7). The other major possibility is regulation of the synthesis of trehalose. The experiments reported in this paper were undertaken to examine this possibility. Fat body has been shown to be the chief site of trehalose synthesis in several species of insects (2, 8). There is evidence that this synthesis occurs by the pathway originally described from yeast (9, 10).