A method for the iodination of insulin and its binding to dissociated mouse mammary cells

The iodination of insulin was accomplished by a modification of the lactoperoxidase method. The use of a low concentration of hydrogen peroxide (1.5 ng/ul) followed by Sephadex gel filtration and purification on a cellulose column yielded iodoinsulin with an activity equal to that of native insulin in stimulation of glucose oxidation in rat epididymal fat cells and with high specific binding to collagenase-dissociated mouse mammary cells from pregnant and lactating mice. Other hormones tested did not displace the binding. Analysis of displacement curves and scatchard plots suggests that both the affinity and the number of sites for insulin binding differ between pregnant and lactating mammary cells.