Table 2.

Effect of addition of human liver microsomal protein to a purified system of b5R and cyt b5, on reduction capacity for NHOH-4-ABP and NHOH-PhIP.^a

Protein Source	Substrate (Reduction velocities; nmol/min)
	NHOH-4-ABP	NHOH-PhIP
HLM	1.02 ± 0.02	1.28 ± 0.001
b5R/cyt b5	2.88 ± 0.01	2.88 ± 0.08
Predicted additive HLM + b5R/cyt b5	3.90 b	4.16 c
Observed HLM + b5R/cyt b5	4.15 ± 0.04 b	3.72 ± 0.11 c

^aAll reactions performed as described in Table 1, using 250 μg HLM (for NHOH-4-ABP) or 1.0 mg HLM (for NHOH-PhIP), and 1.1 nmol b5R/cyt b5 (1:10 stoichiometry), or both enzyme systems in combination (observed activity). Predicted additive activity was derived by adding mean activities for each system alone. Note that total activities are not normalized to mg of protein, in order to more easily detect any enhancement of activity in the purified system following addition of microsomal protein. These results represent data run in duplicate for each condition. Similar results were observed for addition of 1.0 mg of HLM with NHOH-4-ABP as a substrate.

^bNot significantly different by one sample t-test.

^cNot significantly different by one sample t-test.