A peptide substrate for Escherichia coli protein kinase activity in vitro

The phosphorylation in vitro of a series of exogenous peptides by E. coli protein kinases was studied. One of the substrates assayed, the hexapeptide Arg-Gly-Tyr-Ser-Leu-Gly, was found to be significantly phosphorylated at its serine residue. This finding provides the first example of an exogenous substrate utilizable by bacterial protein kinases. The kinetic parameters of the corresponding reaction were determined and the effect of various cations were analyzed. Magnesium, cobalt, manganese and zinc ions were all found to be activators, although to a varying extent. The results were discussed in terms of substrate specificity of bacterial protein kinases.