Identification of storage protein receptor and its precursor in the fat body membrane of Sarcophaga peregrina.

A previous paper (Ueno, K., Ohsawa, F., and Natori, S. (1983) J. Biol. Chem. 258, 12210-12214) showed that a storage protein receptor is present in membranes of the pupal fat body of Sarcophaga peregrina, whereas membranes of the larval fat body contain a cryptic receptor, and that 20-hydroxyecdysone is essential for activation of the cryptic receptor to bind and incorporate the storage protein. The present paper reports that the storage protein receptor is a membrane protein of the pupal fat body with a molecular mass of 120 kilodaltons, and that the cryptic receptor present in membranes of the larval fat body is a precursor of the active receptor with a molecular mass of 125 kilodaltons. It is suggested that when 20-hydroxyecdysone is secreted, it activates the process of conversion of the 125-kDa protein to the 120-kDa protein. Concomitant protein synthesis was not apparently necessary for activation of the storage protein receptor, suggesting that the target of 20-hydroxyecdysone in this case is the fat body membrane.