Objective—To elucidate the functional characteristics
of a highly purified soluble liver insulin receptor in
Sample population—Frozen livers from domestic
cats were obtained commercially.
Procedures—The feline hepatic insulin receptor was
purified from Triton X-100 solubilized plasma membranes
by the use of several chromatography matrices,
including affinity chromatography on an insulin-Sepharose matrix.
Results—The receptor, although not homogeneous,
was purified 3,000-fold. Two silver-stained protein
bands were identified following sodium dodecyl sulfate-
polyacrylamide gel electrophoresis (SDS-PAGE)
with molecular weight of 134,000 and 97,000, which
are similar to insulin receptors isolated from other animals.
This isolated receptor had steady-state insulin
binding by 40 minutes at 24 C. Optimal insulin binding
occurred at pH 7.8 and with 150 mM NaCl. Under
these conditions, a curvilinear Scatchard plot was
obtained with the isolated receptor. Using a 2 bindingsite
model, the feline insulin receptor had a high-affinity
low-capacity site with a dissociation constant (KD;
nM) of 3 and a low-affinity high-capacity site with a KD
of 1,180. The receptor also had tyrosine kinase activity
toward an exogenous substrate that was stimulated
by insulin and protamine.
Conclusions and Clinical Relevance—Many of the
reported characteristics of the liver insulin receptor in
cats are similar to those for the receptor isolated from
other animals and tissues, although some differences
exist. These similarities suggest that characterization
of the feline insulin receptor is important to understanding
insulin resistance in cats with diabetes as
well as in humans with diabetes. (Am J Vet Res