Table 4.

Reaction rates for four Y. pestis enzyme classes comparing -Fe vs. +Fe conditions

	Reaction ratea) (nmol min-1 mL-1); (U mL-1)b)			Reaction ratea) (nmol min-1 mL-1); (U mL-1)b)
Enzyme	+Fe, exp, n = 4e)	-Fe, early, n = 5e)	p-valuef)	+Fe, stat, n = 4e)	-Fe, late, n = 5e)	p-valuef)
Aconitase c)	2.31	1.14	0.019	4.98	1.82	0.008
Pyruvate oxidase c)	167.5	1307	0.0001	463.0	2405	0.0001
Catalase d)	82.5	31.8	0.0001	93.4	29.0	0.0001
Superoxide dismutase d)	887.8	426.9	0.002	448.5	312.5	0.234

^a) Spectrophotometric assays in 96-well microtiter plates were used for the determination of enzyme reaction rates. Total protein concentrations in crude cell lysates were the same for all samples used in a given enzyme assay: aconitase, 0.5 mg/mL; pyruvate oxidase, 0.4 mg/mL; catalase, 0.15 mg/mL; superoxide dismutase, 1.1 μg/mL. ^b) Units ml^-1 was the definition for the superoxide dismutase reaction rate. All assays were performed in duplicate. ^c) Reaction rates from the linear part of the slope of the absorbance change over time. ^d) Reaction rates from endpoint assays. ^e) Number of biological replicates of cell lysates (n); exp: abbreviation for exponential, early: early growth phase equivalent to exp. phase (-Fe); average OD₆₀₀ = 0.66 (+Fe) and OD₆₀₀ = 0.47 (-Fe); stat: abbreviation for stationary growth phase, late: late growth phase equivalent to stat. phase (-Fe); average OD₆₀₀ = 2.0 (+Fe) and OD₆₀₀ = 0.81 (-Fe). True exponential and stationary growth phases were not observed for cell cultures in iron-free media. ^f) p-values were calculated from to comparison of reaction rates (+ Fe vs. -Fe) using a two-tailed t-test method.