Proteomic analysis of iron acquisition, metabolic and regulatory responses of Yersinia pestis to iron starvation

Table 4 Reaction rates for four Y. pestis enzyme classes comparing -Fe vs. +Fe conditions

	Reaction rate^a) (nmol min-1 mL-1); (U mL-1)^b)			Reaction rate^a) (nmol min-1 mL-1); (U mL-1)^b)
Enzyme	+Fe, exp, n = 4^e)	-Fe, early, n = 5^e)	p-value^f)	+Fe, stat, n = 4^e)	-Fe, late, n = 5^e)	p-value^f)
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.

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