Table 2.

Approximate ratios of kinetics factors for interaction of human insulin, IGF-1, and [d-His^B24, Gly^B31, Tyr^B32]-insulin (An) with IR-A and IGF-1R

Ratios were calculated from mean values of the measured parameters. Relative S.D. values were in the range 10–50%; thus, the ratios must be considered as approximate. X and Y represent the values for the ligands listed in individual columns (insulin, IGF-1, and [d-His^B24, Gly^B31, Tyr^B32]). For details, see “Experimental procedures” and Table S1. An, [d-His^B24, Gly^B31, Tyr^B32]-insulin.

Receptor type	Parameter	Insulin/IGF-1	Insulin/An	IGF-1/An
IR-A	Kda	1:88	2.5:1	221:1
	d1b	6.4: 1	3.4: 1	1: 1.9
	Theor. a1X/a1Y =	563: 1	1.4: 1	1: 420
	d1X/d1Y × KdY/KdXc
	ameas.d	1.1: 1	1: 1.1	1: 1.3
	aderived	1.6: 1	1.2: 1	1: 1.3
	Factor site 2 s2X/s2Y =	1: 512	1: 1.5	323: 1
	KdX/KdY × aX/aY × d1Y/d1Xe	1: 352	1: 1.1	323: 1
IGF-1R	Kda	1217: 1	150: 1	1: 8
	d1b	1: 3	1: 3	1: 1
	Theor. a1X/a1Y =	1: 3651	1: 479	8: 1
	d1X/d1Y × KdY/KdXc
	ameas.d	1: 100	1: 15	6.7: 1
	aderived	1: 89	1: 14	6.4: 1
	Factor site 2 s2X/s2Y =	37: 1	30: 1	1: 1.2
	KdX/KdY × aX/aY × d1Y/d1Xe	41: 1	32: 1	1: 1.3

^a Dissociation constants (K_d) are from receptor-binding assays.

^b Ratios of dissociation factors for Site 1 (d1) were derived from the dissociation rate at maximal acceleration.

^c Theoretical ratios of association constants (Theor. a1) were calculated as if the reaction followed the simple model of the law of mass action.

^d Association factor (a) was derived from experimental curves, using the measured rate of dissociation of ¹²⁵I-labeled ligand without the presence of cold ligand (a_meas.), or constants calculated in the model for negative cooperativity (6) were applied (a_derived).

^e Factor Site 2 (s2) is an estimated value to complement the equation, using both association factors (a_meas. upper value and a_derived lower value).