Table 2.

Summary of partial purification of NCA

Purification step	Total protein, mg	Specific activity, fmol/mg per min	Total activity, fmol/min	Yield, %
Isolated nuclei	56	12.9	722	100
supernatant	9.8	63	617	85.5
Peak I	0.17	2,020	343	47.5
Peak II	0.75	242.9	182.2	25.2

Ca²⁺-ATPase activity was determined by measuring P_i produced by ATP hydrolysis. For peak I (fractions 9-17 pooled) and peak II (fractions 24-36 pooled), partial purification was performed in the presence of 1 mM CaCl₂ and 2 mM phenylmethylsulfonyl fluoride, followed by gel-filtration of pooled fractions using Sephadex G-50 fine to eliminate AMP-PNP and NaCl. Blanks were estimated in the same way except that no protein was added, and values (expressed in fmol/mg per min) were corrected accordingly. Addition of trichloroacetic acid before addition of ATP yielded P_i counts equal to blanks. Basal ATPase activity (with 2 mM EGTA and without added calcium) was subtracted from ATP hydrolysis in calcium buffer to yield Ca²⁺-dependent ATPase activity.