High tyrosine-specific protein kinase activity in normal human peripheral blood lymphocytes |
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Authors: | James M Trevillyan Agneta Nordstrom TJuhani Linna |
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Institution: | Central Research and Development Department, E.I. du Pont de Nemours & Co., Inc., Glenolden Laboratory, Glenolden, PA 19036 U.S.A. |
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Abstract: | Tyrosine-specific protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) activity was measured in normal human nonadherent peripheral blood lymphocytes using synthetic peptide substrates having sequence homologies with either pp60src or c-myc. A high level of tyrosine-specific protein kinase activity was found associated with the cell particulate fraction (100 000 × g pellet). High-pressure liquid chromatography and phosphoamino acid analysis of the synthetic peptide substrates substantiated the phosphorylation of tyrosine residues by the particulate fraction enzyme. The human enzyme was also capable of phosphorylating a synthetic random polymer of 80% glutamic acid and 20% tyrosine. Enzyme activity was half-maximal with 22 μM Mg·ATP and had apparent Km values for the synthetic peptides from 1.9 to 7.1 mM. The enzyme preferred Mg2+ to Mn2+ for optimal activity and was stimulated 2–5-fold by low levels (0.05%) of some ionic as well as non-ionic detergents including deoxycholate, Nonidet P-40 and Triton X-100. The enzyme activity was not stimulated by N6;O2′-dibutyryl cyclic AMP (100 μM), N6;O2′-dibutyryl cyclic GMP (100 μM), Ca2+ (200 μM), insulin (1 μg/ml) or homogeneous human T-cell growth factor (3 μg/ml) under the conditions used. Alkaline-resistant phosphorylation of particulate proteins in vitro revealed protein bands with Mr 59 000 and 54 000 suggesting that there are endogenous substrates for the human lymphocyte tyrosine protein kinase. |
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Keywords: | Tyrosine specificity Protein kinase Phosphorylation (Human lymphocyte) PMSF phenylmethylsulfonylfluoride Hepes 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid Chaps 3-[(3-cholamidopropyl)dimethylammonio]propanesulfonate |
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