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A cytosolic protein tyrosine kinase in rat adipocytes
Author(s) -
Shisheva Assia,
Shechter Yoram
Publication year - 1992
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(92)80171-c
Subject(s) - cytosol , tyrosine kinase , chemistry , protein kinase a , tyrosine , microbiology and biotechnology , biochemistry , kinase , biology , enzyme , signal transduction
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 PolyGlu 4 Tyr whith high efficiency at a rate of 20 ± 2 pmoI PTyr/20μg PolyGlu 4 Tyr/20 min/μg 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 Co 2+ rather than by Mn 2+ , and it was not inactivated by N ‐ethylmaleimide. The enzyme was extremely sensitive to inhibition by staurosporine (ID 50 = 3 nM) as opposed to IRTK (ID 50 = 8μM). 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.