USE OF SYNTHETIC PEPTIDES AND COPOLYMERS TO STUDY THE SUBSTRATE-SPECIFICITY AND INHIBITION OF THE PROTEIN-TYROSINE KINASE PP60(C-SRC)

The ability of synthetic peptides and polypeptides to act as substrate s and/or inhibitors of pp60(c-scr) was examined. The random copolymer, poly(K4Y) had a threefold lower specificity than poly(E(4)Y). Peptide s containing lysine vs. glutamate were also found to have a lower subs trate specificity (V-max:K-m ratio). In order to assess the substrate specificity of acidic peptides, an assay protocol using DEAE-membranes was developed. Peptides containing a (YXE)(5)YXD motif (X = G, A, V, P, or norvaline) were tested as inhibitors and substrates of pp60(c-sc r). The glycine-containing peptide was the best substrate having a spe cificity 16 000-fold higher than (5)Val-angiotensin II, the most commo nly used peptide substrate. Most of the peptides, except for the proli ne containing peptide, had K-i values of 20-100 mu M. In a series of ( XGE)(5)XGD peptides, where X = Y or F, tyrosine at position 10 was fou nd to be the preferred site for accepting a phosphate. Analogs in whic h the glycine was replaced with alanine indicated that loss of flexibi lity around position 10 was detrimental to substrate specificity. Resu lts suggest that conformational requirements of the peptides tested wa s important and substrate specificity was a more sensitive parameter t han binding as measured by K-i values.