In vivo kinetics of pyrrolidonecarboxylic acid formation in selected silkmoth chorion proteins.

The protein products from one of the two major silkmoth chorion multigene families contain blocked NH2 termini. The blocked residue has been identified as pyrrolidonecarboxylic acid. Its formation occurs post-translationally, by modification of NH2-terminal glutamine, after removal of a 20-residue-long "signal peptide." Pyrrolidonecarboxylic acid formation begins within minutes after polypeptide chain termination and is largely, although not entirely, complete by 60 min. Pyrrolidonecarboxylic acid thus appears to be formed both within the cell and in the extracellular chorion. Another class of minor chorion proteins also appears to contain pyrrolidonecarboxylic acid.