title: Functional and structural differences in human and rat-derived insulin receptors: characterization of the beta-subunit kinase activity.
abstract: We studied the kinase activity of partially purified insulin receptor preparations from various rat and human tissues. Time courses for in vitro autophosphorylation were determined, and times to reach half-maximal (t1/2 max) and maximal (tmax) 32P incorporation were compared. Insulin receptors from rat muscle, liver, and fat had a t1/2 max of 7-10 min and a tmax of 60 min; human-derived insulin receptors had a t1/2 max in excess of 30 min and a tmax of 120 min. A spectrum of autophosphorylation time courses was present in human tissues; placenta-derived receptors exhibited a t1/2 max of 13 min while receptors from monocytes and fibroblasts had t1/2 max values of 60 and 80 min, respectively. The ATP Km for autophosphorylation of human-derived receptors was 5-fold greater than that of rat-derived receptors (266 +/- 27 vs. 48 +/- 8 microM, respectively). In contrast, when the receptors were first maximally prephosphorylated, the ATP Km values for substrate phosphorylation of human- and rat-derived receptors were equivalent (12.5 and 11.4 microM). Kact values for Mn were comparable in both human- and rat-derived adipocyte receptors. In addition to the functional differences between species, the apparent mol wt of the beta-subunit of rat-derived receptors (96,000) was consistently greater than that of human-derived receptor beta-subunits (93,000). In contrast to these in vitro findings, the ability of insulin to stimulate receptor kinase activity in isolated adipocytes was rapid, with a maximal effect by seconds. This was comparable for both rat and human tissues, suggesting that the in vitro autophosphorylation differences may not govern kinase activity in vivo.
authors.affiliation: Department of Medicine, University of California-San Diego, La Jolla 92093.
authors.forename: D J
authors.initials: DJ
authors.lastname: Brillon
authors.forename: R R
authors.initials: RR
authors.lastname: Henry
authors.forename: H H
authors.initials: HH
authors.lastname: Klein
authors.forename: J M
authors.initials: JM
authors.lastname: Olefsky
authors.forename: G R
authors.initials: GR
authors.lastname: Freidenberg
mesh_terms: D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008297:Male; D009132:Muscles / Q000378:metabolism; D009928:Organ Specificity; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011972:Receptor, Insulin / Q000302:isolation & purification / Q000378:metabolism*; D013045:Species Specificity
chemical_list: D046911:Macromolecular Substances; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin