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A Kowalski

Publications and source records attributed to A Kowalski.

At least 55 records · Page 3Linked to original sources
PubMed1983

Dephosphorylation of the hepatic insulin receptor: absence of intrinsic phosphatase activity in purified receptors.

We have compared here the reversibility of phosphorylation of insulin receptors either partially purified by lectin chromatography, or highly purified by specific immunoprecipitation with anti-receptor antibodies. We found that the beta subunit of partially purified insulin receptors was rapidly dephosphorylated (t 1/2 = 15 min). In contrast, the level of phosphorylation of immunoprecipitated receptors remained unchanged for up to 4 hours at 37 degrees C. However, cytosolic phosphatases, which are inhibited by vanadate, were able to induce a complete dephosphorylation of immunoprecipitated receptors. These results show that 1. phosphorylation of insulin receptors is reversible; and 2. no phosphatase activity is contained in the insulin receptor structure itself.

Animals↗
PubMed1983

Two different protein kinase activities are associated with the insulin receptor.

In intact rat hepatocytes insulin stimulates the phosphorylation of the beta-subunit of its receptor exclusively on serine residues, which are also phosphorylated in the absence of insulin. In contrast, in partially purified insulin receptors derived from these same cells and in highly purified insulin receptors obtained by immunoprecipitation with anti-receptor antibodies, the receptor beta-subunit is phosphorylated solely on tyrosine residues. For both cell-free systems, insulin's stimulatory action on receptor phosphorylation leads to an increase in phosphotyrosine. When partially purified receptors were used to phosphorylate two exogenous substrates, casein and histone, insulin was found to stimulate the phosphorylation of both tyrosine and serine. However, the basal and insulin-stimulated kinase activity of immunoprecipitated receptors was only tyrosine-specific. From these observations we propose that the insulin-receptor complex consists of two different insulin-stimulatable kinase activities: (1) a tyrosine-specific kinase, which is a constituent of the insulin-receptor structure and whose activation is likely to be the first post-binding event in insulin action; and (2) a serine-specific kinase, which is closely associated with the receptor in the cell membrane.

Animals↗
PubMed1983

Cancer of mamma virilis.

The authors describe a patient who, because of false shame, reported for treatment in the course of an advanced neoplastic process of the mamma. Combined treatment consisting of surgical castration, hormonotherapy and irradiation was applied. In about 30 per cent of patients thus treated a temporary remission or inhibition of the neoplastic process has been observed.

Breast Neoplasms↗
PubMed1983

Receptor-mediated phosphorylation of the hepatic insulin receptor: evidence that the Mr 95,000 receptor subunit is its own kinase.

Insulin stimulates the phosphorylation of its own receptor. In the work reported here, the kinase activity responsible for the insulin-stimulated phosphorylation of the insulin receptor was localized. In a first approach, partially purified insulin receptors derived from normal rat hepatocytes were immunoprecipitated with antibodies specific for the insulin receptor; thereafter, the immunoprecipitates were incubated with [gamma-(32)P]-ATP in the absence or presence of insulin (1 muM). NaDodSO(4)/polyacrylamide gel electrophoretic analysis of the immunoprecipitates under reducing conditions revealed autophosphorylation of the beta subunit (M(r) 95,000) of the insulin receptor; the alpha subunit (M(r) 130,000) was not phosphorylated. Further, insulin specifically increased 3- to 4-fold the labeling of its own receptor beta subunit, indicating that anti-receptor antibodies precipitate a functional and insulin-stimulable protein kinase that appears to be independent of cyclic AMP and calcium. To localize more precisely the insulin receptor-related kinase activity, we searched for an ATP-binding site on solubilized insulin receptors. By using covalent labeling with oxidized [alpha-(32)P]ATP, a labeled polypeptide with precisely the same electrophoretic mobility as that of the beta subunit of the insulin receptor (M(r) 95,000) was specifically immunoprecipitated with anti-receptor antibodies. Further, its appearance was prevented when the immunoprecipitation was preceded by incubation with unlabeled insulin. In conclusion, we have shown that an insulin-stimulated phosphorylation site and an ATP-binding site coexist on the beta subunit of the insulin receptor. The simultaneous presence of these two sites on the same receptor subunit indicates that the insulin receptor acts as its own protein kinase.

Adenosine Triphosphate↗