Abstract
The membrane protein of pteridine granules produced in the larval hypodermis of a strain of normal silkworm larvae was isolated and its chemical composition analysed. This protein is composed almost entirely of protein and lipid. The protein content makes up 65-68% of the dry weight, the lipid content, 31-33% and the carbohydrate content, 1.1-1.4%. The amino acid composition of the membrane protein of normal granules is shown. Essentially this amino acid composition is very similar to that of structural membrane proteins from other species.
Using several different solvents, the solubility of the membrane protein was tested. The membrane protein is readily soluble in sodium dodecyl sulfate urea solution. It was found that the membrane protein dissociates into electrophoretically and ultracentrifugally homogeneous subunits and thus it is inferred that the membrane protein of normal pteridine granules consists of a single homogeneous structural protein having a molecular weight of about 20, 000.
