title: Characterization of four tyrosine protein kinases from the particulate fraction of rat spleen.
abstract: Four distinct tyrosine protein kinases active on poly(Glu4,Tyr1) and angiotensin II, and operationally termed TPK-I, TPK-IIA, TPK-IIB and TPK-III have been resolved and partially purified from rat spleen particulate fraction by combining DEAE-Sepharose, heparin-Sepharose, phosphocellulose and polylysine-agarose chromatographies. Once partially purified all of them are free of Ser/Thr-specific protein kinase activity as judged using casein, histones, protamine and the peptide Arg-Arg-Ala-Ser-Val-Ala as substrates. TPK-I (apparent molecular mass 64 kDa, by gel filtration) and TPK-IIA (54 kDa) share several properties, including substrate specificity and stimulation by heparin; the latter however is much more responsive to polylysine then the former (10- and 3-fold maximum stimulation, respectively). Conversely TPK-IIB (51 kDa) is markedly inhibited by heparin and it is also characterized by its unique substrate specificity: unlike the other three tyrosine protein kinases it by far prefers the tetrapeptide Glu-Tyr-Ala-Ala over the decapeptide Asp-Ala-Glu-Tyr-Ala-Ala-Arg-Arg-Arg-Gly and readily phosphorylates band-3 protein of red cell membrane. The unusual preference for Mg2+ over Mn2+ as activator and the capability to phosphorylate calmodulin distinguish TPK-III (61 kDa) from the other isoenzymes. Moreover TPK-III is insensitive to heparin and polylysine and is inhibited by quercetin much more efficiently than the other enzymes (I50 = 10 microM). Upon incubation with [gamma-32P]ATP, TPK-I, TPK-IIA and TPK-III give rise to alkali-stable radiolabeled components of 61, 55 and 52 kDa respectively, as evaluated by PAGE/SDS. In every case such a radiolabeling takes place also in the presence of a large excess of phosphorylatable substrate (angiotensin II) while it is readily reversed by isotopic dilution with 10-fold excess unlabeled ATP, supporting the view that it represents an autophosphorylation process. No (auto)phosphorylation product(s) could be detected in TPK-IIB even if its amount, in terms of catalytic activity, was 10-fold higher than that of the others.
authors.affiliation: Istituto di Chimica Biologica, Universitàa di Padova e Centro delle Biomembrane del CNR, Italy.
authors.forename: A M
authors.initials: AM
authors.lastname: Brunati
authors.forename: L A
authors.initials: LA
authors.lastname: Pinna
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002147:Calmodulin / Q000494:pharmacology; D002846:Chromatography, Affinity; D004789:Enzyme Activation / Q000187:drug effects; D006493:Heparin / Q000494:pharmacology; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000145:classification / Q000302:isolation & purification*; D011794:Quercetin / Q000494:pharmacology; D051381:Rats; D013154:Spleen / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D002147:Calmodulin; D006493:Heparin; D011794:Quercetin; D011505:Protein-Tyrosine Kinases