TABLE 3.

Heme reduction and ferrous heme-NO buildup of wild-type and mutant nNOS

All reactions were carried out at 10 °C in a stopped-flow spectrophotometer as described under “Experimental Procedures.” The values for heme reduction in wild type and E762N are the means ± S.D. of 7–10 individual reactions and are representative of experiments done with two enzyme preparations. Rate constants for heme-NO complex buildup were determined during the initial phase of NO synthesis. The numbers in parentheses indicate the percentage of absorbance change for each phase. ND, not detected; WT, wild type.

Enzyme	Heme reduction		Heme-NO complex buildup
	Ca2+-initiated	NADPH-initiated
	s−1		s−1
nNOS WT	4.2 ± 0.3	4.6 ± 0.4	k1 = 9.4 (60%)
			k2 = 1.5 (40%)
E762N	1.7 ± 0.16	1.2 ± 0.1	k1 = 0.34 (100%)
			k2 = ND