Phosphorylation of synthetic peptides by a tyrosine protein kinase from the particulate fraction of a lymphoma cell line.

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Abstract
The particulate fraction from a Moloney murine leukemia virus-transformed mouse lymphoma cell line, LSTRA, contained a high level of tyrosine protein kinase activity. When this fraction was incubated with [.gamma.-32P]ATP in the presence of 10 mM MnCl2, hydrolyzed and assayed, 70-80% of the radioactivity recovered in phosphoamino acids was in phosphotyrosine. Gel electrophoresis of the proteins showed that a large portion of the 32P was in a single protein with a MW of .apprx. 58,000. The phosphorylated residue in this protein was identified as phosphotyrosine. Detergent extracts of the particulate fraction from LSTRA cells contained both the 58,000 MW protein and the enzyme responsible for its phosphorylation. These extracts catalyzed the phosphorylation of the tyrosine residue in the synthetic peptide, Ile-Glu-Asp-Asn-Glu-Tyr-Thr-Ala-Arg-Gln-Gly, corresponding to the sequence around the tyrosine that is phosphorylated in pp60src; the Km for the peptide in this reaction was 5 mM. High-performance liquid chromatography was used to assay for this phosphorylation. A 2nd peptide was synthesized that contained 2 additional arginine residues whose presence permitted the phosphorylation of the peptide to be measured by a simple assay using phosphocellulose paper. The Km for this peptide was 3-4 mM, indicating that the presence of the additional arginine residues did not alter the apparent affinity of the kinase for the peptide.