Table 1.

EC₅₀ Values of Insulin, Proinsulin, IGF-2, IGF-2 Precursors, and IGF-1 for IR-A, IR-B, and IGF-1R

	IR-A	IR-B	IGF-1R	References
Insulin	0.91 ± 0.3	1.0 ± 0.4	nd	Frasca et al. (32)
	nd	nd	>30	Pandini et al. (2)
	0.40 ± 0.10	0.49 ± 0.05	>1000	Sciacca et al. (33)
	nd	nd	383 ± 27	Versteyhe et al. (34)
	1.57 ± 0.33	nd	nd	Rajapaksha et al. (35)
	2.7 ± 0.6	2.6 ± 0.7	nd	Pierre-Eugene et al. (36)
Proinsulin	4.5 ± 0.6	31.0 ± 6.3	>100	Sacco et al. (37)
IGF-2	3.3 ± 0.4	36.0 ± 3.8	nd	Frasca et al. (32)
	nd	nd	0.6	Pandini et al. (2)
	nd	nd	13.1 ± 0.7	Versteyhe et al. (34)
	15.2 ± 0.2	nd	nd	Rajapaksha et al. (35)
	4 ± 0.4	nd	3.4 ± 0.2	Ziegler et al. (38)
pro-IGF-2	nd (<IGF-2)	nd	nd	Marks et al. (39)
big-IGF-2	nd (≈IGF-2)	nd	nd
IGF-1	>30	>30	0.2 ± 0.3	Pandini et al. (2)
	nd	nd	1.49 ± 0.14	Versteyhe et al. (34)
	34 ± 13	50 ± 13	nd	Pierre-Eugene et al. (36)

Abbreviations: EC₅₀, ligand concentration (nM) required to achieve 50% of maximal receptor activation; nd, not determined.