Table 1.

Typical values of binding affinities (K_d values) of insulin, IGF-1, and IGF-2 for human IR-A (in membranes of human IM-9 lymphocytes), human IR-B or human IGF-1R (in membranes of mouse fibroblasts) measured in our laboratory using ¹²⁵I-labeled insulin or ¹²⁵I-labeled IGF-1 as tracers.

Hormone/receptor	IR-A (nM)	IR-B (nM)	IGF-1R (nM)
Human insulin	0.2–0.5a,b	0.3–0.7a	290a
Human IGF-1	24b	225b	0.2–0.3a,c
Human IGF-2	2.9–3.0b,c	35b	2.3b

^aAdapted from Ref. (23).

^bAdapted from Ref. (24).

^cAdapted from Ref. (25).