Identification and initial characterization of insulin receptor-like immunoreactivity in human plasma.
With a two-step purification procedure employing sequential affinity chromatography with insulin receptor monoclonal antibody followed by wheat germ agglutinin, we isolated from the plasma of two healthy individuals a material that reacted in a specific RIA for insulin receptors. This material produced dilution curves that were parallel to a human placental insulin receptor standard. This material also bound [125I]insulin; competition-inhibition curves revealed an ED50 of 0.3 nM, a value similar to that obtained with placental insulin receptors. The material purified from plasma was then labeled with [125I] Bolton-Hunter reagent, followed by polyacrylamide gel electrophoresis under reducing conditions and autoradiography. A band at 135 kilodaltons (kDa) was observed, corresponding to the alpha-subunit of the insulin receptor. Several bands ranging from 82-46 kDa were also detected. One or more of these fragments had intrinsic autophosphorylation activity, but only the 82-kDa band activity was responsive to insulin. In addition, employing the synthetic substrate poly(Glu4:Tyr1), no insulin-sensitive tyrosine kinase activity was present. These studies demonstrate, therefore, that insulin receptor-derived material is present in human plasma. This material retains high affinity insulin binding, but has an altered beta-subunit that is devoid of insulin-responsive tyrosine kinase activity.
Pezzino
V
V
Cattedra di Scienza delle Costituzioni, Universita di Catania, Italy.
Papa
V
V
Costantino
A
A
Frittitta
L
L
Russo
P
P
Goldfine
I D
ID
Vigneri
R
R
D006801:Humans; D007328:Insulin / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000097:blood; D011863:Radioimmunoassay; D011972:Receptor, Insulin / Q000032:analysis* / Q000276:immunology / Q000502:physiology
D007328:Insulin; D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin