Table 1

Effects of substitution of the TM regions with corresponding portion of the β₁AR on the ligand-binding characteristics of the β₂AR

Receptor	¹²⁵I-CYP (K_d)	Agonist (K_i)
Receptor	¹²⁵I-CYP (K_d)	TA-2005	Isoproterenol	Compound II	Compound III
	pm	nm
WT-β₂AR	73	12^1-a	900^1-a	170	6300
	(43–120)	(1.8–82)	(200–4000)	(130–230)	(4800–8400)
CH1	86	9.2	1400	190	7900
	(44–170)	(7.2–12)	(440–4600)	(98–370)	(5300–12000)
CH2	100	78^1-b	1000	130	3800
	(63–170)	(22–280)	(530–1900)	(79–210)	(1400–10000)
CH3	150	96^1-b	560	320^c	8000
	(100–210)	(15–610)	(190–1600)	(120–900)	(5000–13000)
CH4	280^c	240^1-b	400^c	220	5200
	(280–420)	(84–690)	(230–710)	(79–590)	(1700–16000)

The binding of ligands to the WT- and CH-βARs was measured by competition with 50 pm ¹²⁵I-CYP. The data were analyzed using the nonlinear least-squares regression computer program as described in Experimental Procedures. The results are shown as the means and 95% confidence limits of three to four separate experiments.

↵1-a Data from Kikkawa et al. (1997) for the clarity.
↵1-b p < 0.01, ^c p < 0.05, significantly different from WT-β₂AR.