TABLE 2.

Purification of wild-type RibC and mutant RibC820 from cell extracts of overproducing E. coli strains

Purification step	Wild-type RibC		RibC820
	Flavokinase activitya	Purification (fold)	Flavokinase activity	Purification (fold)
Cell extract	70	1	1	1
(NH4)2SO4 (40–70% [wt/vol]) purification	140	2	2	2
Cation exchange	580	8	6	6

^aMeasured in a final volume of 1 ml of potassium phosphate (pH 7.5) containing 50 μM riboflavin, 3 mM ATP, 15 mM MgCl₂, and 10 mM Na₂SO₃ and expressed as nanomoles of FMN produced per minute per milligram of protein. FAD synthetase activity could not be exactly measured because exogenous, highly purified 5′-FMN was not accepted as a substrate.