The influence of tracers on insulin binding to human erythrocytes.

We studied insulin binding to human erythrocytes using two different 125I-insulin-tracers. Erythrocytes of 8 normal subjects were examined using [mono-125II-(Tyr A 14)insulin as tracer. Three of these erythrocyte preparations were examined simultaneously using [125I]insulin, which was randomly iodinated by the chloramine-T-method. Data were analysed by a computerized non-linear least-squares procedure both on the basis of one and two class receptor models. Only the one class receptor model yielded consistent results. When the two class receptor model was applied the low affinity branch of the Scatchard plot was not reproducible. On the basis of the one class receptor model the number of receptor sites was lower (R0 = 0.046 +/- 0.006 nmol/l equivalent to 6.3 +/- 0.8 receptors/erythrocyte) with [mono-125I-(Tyr A 14)]insulin as compared to [125I]insulin randomly iodinated by the chloramine-T method (R0 = 0.070 +/- 0.008 nmol/l equivalent to 9.6 +/- 1.1 receptors/erythrocyte). Conversely, the affinity of the [mono-125I-(Tyr A 14)]insulin was higher (Ka = 2.6 +/- 0.3 x 10(9) l . mol-1 vs. 1.9 +/- 0.2 x 10(9) l . mol-1.