title: A cytosolic protein tyrosine kinase in rat adipocytes.
abstract: Previous studies suggested that insulin receptor tyrosine kinase (IRTK) is the sole tyrosine kinase in rat adipocytes. We now report that this cell type also contains a cytosolic soluble protein tyrosine kinase (CytPTK) which is not related to IRTK. The enzyme phosphorylated PolyGlu4Tyr with high efficiency at a rate of 20 +/- 2 pmol PTyr/20 micrograms PolyGlu4Tyr/20 min/micrograms cytosolic protein. Upon gel filtration chromatography the enzyme activity was eluted as a single peak corresponding to a molecular mass of 53 +/- 3 kDa. Unlike IRTK, CytPTK activity was supported by Co2+ rather than by Mn2+, and it was not inactivated by N-ethylmaleimide. The enzyme was extremely sensitive to inhibition by staurosporine (ID50 = 3 nM) as opposed to IRTK (ID50 = 8 microM). In addition, CytPTK (but not IRTK) was largely activated by vanadate ions. Agents which affect the serine/threonine phosphorylation state of cell proteins did not alter CytPTK activity when subjected to intact adepocytes. In a cell-free system CytPTK activity was largely reduced by pretreatment with immobilized alkaline phosphatase at physiological pH. The possibility that CytPTK participates in insulin-independent regulation of glucose metabolism is suggested.
authors.affiliation: Department of Hormone Research, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Shisheva
authors.forename: Y
authors.initials: Y
authors.lastname: Shechter
mesh_terms: D000273:Adipose Tissue / Q000166:cytology / Q000201:enzymology*; D000818:Animals; D002850:Chromatography, Gel; D003600:Cytosol / Q000201:enzymology*; D005947:Glucose / Q000378:metabolism*; D008297:Male; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000302:isolation & purification / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000378:metabolism
chemical_list: D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D005947:Glucose