Protein kinase activity of the insulin receptor in human circulating and cultured mononuclear cells

In lectin-purified receptor preparations from human monocyte-like cell (U-937), insulin (10(-7)M) stimulated phosphorylation of the 95,000 dalton subunit of its own receptor. In addition, insulin stimulated phosphorylation of exogenously added substrates like casein, (T,G)-A--L, and histones. Phosphorylation of the synthetic peptide (T,G)-A--L indicates the presence of at least one insulin-dependent tyrosine kinase in these cell extracts. Insulin receptor preparations from freshly isolated human mononuclear blood cells were also shown to possess insulin-dependent casein and (T,G)-A--L kinase activity. Phosphorylations in these systems are specific for insulin and dependent on insulin concentration. A simple and rapid method is described that is relevant for clinical investigations of early postbinding events.