Trypsin and α-chymotrypsin effects on masked insulin receptors were studied. Phospholipase
C treatment, incubation in a high ionic strength buffer or solubilization were used
as alternative procedures for the unmasking of insulin receptors. These three methods
expose receptor structures which are inaccessible to insulin in the current experimental
conditions of binding assays without any significant change in binding affinity. Both
exposed and masked receptors proved to be equally sensitive to trypsin and α-chymotrypsin
degradation. At 25°C, about 5 μg trypsin/ml for 50 min or 80 μg α-chymotrypsin/ml
for 200 min were necessary in each case to cause a 50% inhibition of the binding of
125I-iodo insulin to microsomes.
The results suggest that masked receptors are only nonfunctional to bind insulin but
they are not located in compartments inaccessible to molecules present in the medium.
Insulin Receptors
-
Unmasking
-
Submaxillary Gland
