TABLE 1.

Purification of the P. aerophilum nitrate reductase^a

Purification step	Total amt of protein (mg)	Total activity (U)	Sp act (U/mg)	Yield (%)	Purification (fold)
Membrane fraction	78	191	2.4	100	1
Triton X-100 extract	33	193	7.9	100	3
Q-Sepharose	5.5	134	24.5	69	10
Hydroxyapatite	0.8	77	100	40	42
Mono-Q	0.01	3	326	1.6	137

^aThe activity was measured at 75°C. One unit of enzyme activity is defined as 1 μmol of nitrate reduced per min.