Deletion of approximately 10 kDa from the carboxyl terminus of a soluble approximately 48-kDa insulin receptor protein-tyrosine kinase results in slower rates of diphosphorylation of a series of dodecapeptide substrates. An assessment by 1H NMR.

Autophosphorylation of a soluble approximately 48-kDa derivative of the insulin receptor protein-tyrosine kinase is accompanied by an increase in its specific activity towards exogenous substrates. In the present study, we have utilized 1H NMR to compare the order and rate of mono- and diphosphorylation of multiple tyrosine residues in a series of synthetic dodecapeptide substrates (based on the receptor sequence, which includes major sites of autophosphorylation (RRDIYETDYYRK), with substitution(s) at positions 6 and/or 7 based on residue size and/or charge) by the approximately 48-kDa enzyme and by a approximately 38-kDa enzyme generated by tryptic deletion of approximately 10 kDa from the carboxyl terminus of the approximately 48-kDa protein. Both enzymes exhibit a marked order and progression of phosphorylation of peptide tyrosine residues; for each peptide, phosphorylation initiates and proceeds to completion first on tyrosine 9, followed by phosphorylation on tyrosine 10. Although removal of the carboxyl terminus does not affect the rate of monophosphorylation of these peptides on tyrosine 9, the smaller enzyme exhibits a slower rate of diphosphorylation (at tyrosine 10), as compared with the approximately 48-kDa enzyme.