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  • Title: A cytosolic protein tyrosine kinase in rat adipocytes.
    Author: Shisheva A, Shechter Y.
    Journal: FEBS Lett; 1992 Mar 23; 300(1):93-6. PubMed ID: 1547896.
    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.
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