Table 2.

Relative binding specificities of cyclic nucleotide analogs measured with various cGMP and cAMP immunoassays as described under “Methods” section

Analog	Specificity ENZO cAMP-EIA	Specificity IBL cAMP-RIA	Specificity ENZO cGMP-EIA	Specificity IBL cGMP-RIA	Specificity Cayman cGMP-EIA
cAMP	1.00	1.00
cGMP			1.00	1.00	1.00
2′-dcGMP			0.052
Rp-cGMPS			0.0027	0.10
2′-dcAMP	0.034
8-Br-cGMP (15)			4.90	0.20	0.005
Rp-cAMPS (7)	0.68	0.67
8-Br-cAMP (4)	0.004	0.026
Rp-8-Br-cAMPS (12)	0.003
6-MB-cAMP (1)	0.004	0.012
6-Bnz-cAMP (2)	0.006	0.009
8-pCPT-cGMP (16)			2.40	0.30	0.0008
8-pCPT-cAMP (5)	0.0005
8-Br-PET-cGMP (22)			0.10	0.015	0.016
Rp-8-Br-PET-cGMPS (23)			0.002	0.011
8-pCPT-2′-OMe-cAMP (10)	0.0003	0.0066	0.0002	<10−4
Sp-5,6-DCl-cBIMPS (11)	<10−4	0.005
IBMX (26)	<10−5	<10−4	<10−6	<10−6	<10−5

The analogs are ordered according to their lipophilicity (see Table 4). Specificity is expressed as EC_{50cGMP or cAMP}/EC_50Analog. The absolute EC50 binding constants for acetylated cAMP in [M] are 7.62 × 10⁻¹⁰ (ENZO) and 5.8 × 10⁻⁹ (IBL); for acetylated cGMP in [M]: 2.27 × 10⁻¹⁰ (ENZO), 1.8 × 10⁻⁹ (IBL) and 3.9 × 10⁻¹⁰ (Cayman)