Table 1. Purification of HDH V .

Fraction	Step	Volume (ml)	Protein (mg)	DNA helicase activity
				Total (U)	Specific (U/mg)
	Nuclear extract	750	3800	N.D.
I	Ammonium sulfate precipitate	550	2100	N.D.
II	Bio-Rex 70	250	90	N.D.
III	Ammonium sulfate precipitate	60	50	N.D.
IV	Heparin–Sepharose	35	6	260 000	43 000
V	Q-Sepharose	90	1.5	192 000	128 000
VI	ssDNA Sepharose	15	<0.1	91 500	>1 000 000

N.D., not determined.