J. Biol. Chem., Vol. 261, Issue 31, 14361-14364, Nov, 1986
Structural differences between liver- and muscle-derived insulin receptors in rats
CF Burant, MK Treutelaar, NE Block and MG Buse
The structure of insulin receptors, solubilized from rat skeletal muscle
and liver, was studied. The alpha subunit was identified by specific
cross-linking to A14 125I-insulin with disuccinimidyl suberate. Muscle- and
liver-derived alpha subunits migrated on sodium dodecyl
sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with a Mr of 131,000
and 135,000, respectively. There was no significant difference in insulin
binding affinity. Treatment of cross-linked, immunoprecipitated receptors
with either neuraminidase or endoglycosidase H decreased the Mr of muscle-
and liver-derived alpha subunits but did not affect the difference in Mr.
Autophosphorylated beta subunits migrated with a Mr of 98,000 for muscle
and 101,000 for liver. After partial V8 digestion of autophosphorylated,
immunoprecipitated receptors the major phosphopeptide fragment migrated on
SDS-PAGE at Mr 57,000 from muscle and 60,000 from liver. Glycosidase
digestion of autophosphorylated receptors suggested that Mr heterogeneity
was due in part to differences in the sialic acid content of beta subunits.
Muscle and liver are the major target organs of insulin; the apparent
heterogeneity of insulin receptor structure may be relevant to
tissue-specific differences in insulin action.
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