TABLE 4.

Internal competition experiments for hCGβ and LC Iβ single and double mutants

LC Iβ is an analog containing 4 residues of hLHβ (residues 2, 8, 10, and 15) with the remaining components hCG. β-Subunit mutations include N77C, F64C, and A83C. In all analogs that contain βC26A, the β-subunit has the cysteine at position 26 replaced by alanine. The α-subunit contains a cysteine in place of serine 43 in all assays. Analogs were co-transfected into COS-7 cells and quantified in A113/¹²⁵I-B110 assays. “Total dimer” represents the total amount of dimer detected. “Cross-linked dimer” represents the amount of heterodimer that remained after pH 2 treatment, 30 min at 37 °C. ND, not determined.

	Analogs	Total dimer	X-linked dimer	% X-linked dimer
				%
1	hCGβ	9.73 ± 1.79	0.70 ± 0.06	7.2
2	hCGβ C26A	5.20 ± 0.71	5.98 ± 0.24	100
3	hCGβ N77C	8.70 ± 0.60	0.64 ± 0.14	7.4
4	hCGβ N77C C26A	0.15 ± 0.00	0.15 ± 0.00	ND
5	hCGβ F64C	6.89 ± 1.40	0.62 ± 0.05	9.0
6	hCGβ F64C C26A	0.24 ± 0.02	0.22 ± 0.03	ND
7	hCGβ A83C	8.41 ± 0.70	0.55 ± 0.06	6.5
8	hCGβ A83C C26A	0.13 ± 0.00	0.11 ± 0.02	ND
9	LC Iβ	14.23 ± 0.45	0.94 ± 0.06	6.6
10	LC Iβ C26A	13.33 ± 3.28	13.17 ± 0.91	98.8
11	LC Iβ N77C	3.54 ± 0.99	0.29 ± 0.01	8.2
12	LC Iβ N77C C26A	1.27 ± 0.06	1.36 ± 0.02	100
13	LC Iβ F64C	2.90 ± 0.47	0.37 ± 0.03	12.8
14	LC Iβ F64C C26A	2.66 ± 0.46	2.88 ± 0.26	100
15	LC Iβ A83C	2.58 ± 0.27	0.15 ± 0.00	5.8
16	LC Iβ A83C C26A	0.70 ± 0.01	0.64 ± 0.04	91.4