Table 1

Purification of HDCPase in rabbit serum

Purification step	Fraction^1-a	Protein	Activity nmol DCP/30 min/ml fraction		Yield (%)		Specific activity nmol DCP/30 min/mg protein		Purification factor
			Ca⁺⁺	EDTA	Ca⁺⁺	EDTA	Ca⁺⁺	EDTA	Ca⁺⁺	EDTA
			dep	res	dep	res	dep	res	dep	res
	mg protein/ml fraction
Serum	–	70.3	73,300	1,850	100	100	1,043	26	1.0	1.0
First centrifugation	L	0.9	35,930	70	49	4	39,920	78	38.3	3.0
	S	41.9	9,740	1,650	13	89	232	39	0.2	1.5
Second centrifugation	SS	39.0	5,020	1,550	7	84	129	40	0.1	1.5
Sephacryl-DEAE	SS2	16.0	410	1,600	1	86	26	100	0.02	3.8
	SS25	11.8	20	330	0.03	18	17	28	0	1.1
	SS26	10.0	ND^1-b	520	–	28	ND	52	–	2.0

The purification process was performed independently in triplicate, after which the three groups of fractions were pooled and HDCPase and amount of protein were assayed. The fractions were obtained as explained in Materials and Methods. The purification factor was calculated from the ratio between the specific activities of each fraction and the specific activity of serum. Calcium-dependent activity (Ca⁺⁺ dep) was calculated as the difference between the activity exhibited by the samples in the presence of 2.5 mM Ca⁺⁺ and that recorded in the presence of 5 mM EDTA. EDTA-resistant activity (EDTA res) was regarded as the activity exhibited by the samples in the presence of 5 mM EDTA.

↵1-a Fractions L, S, and SS were obtained by ultracentrifugation as is described in Materials and Methods. Fractions SS2, SS25, and SS26 were obtained as is shown in Fig. 2.
↵1-b ND, not detected in the assayed conditions.