Table 1.

Titration of sulfhydryl groups in WT and mutant opsins under denaturing conditions by using PDS

Mutant	Fraction*	mol of PDS per mol of opsin
		Found	Expected number for (1) or (0) disulfide bond
WT	F1	6.1  ±  0.2	6.0 (1)
C110A	F1	6.0  ±  0.2	7.0 (0)
	F2	4.5  ±  0.1	5.0 (1)
C185A	F1	4.9  ±  0.3	5.0 (1)
C187A	F1	4.9  ±  0.4	5.0 (1)
	F2	5.1  ±  0.3	5.0 (1)

^*F1 eluted with buffer J (no salt); F2 eluted with buffer K (containing salt).