TABLE 1.

Enzymatic activity of purified recombinant wild type and mutated His-APAs Shown are the enzymatic activity (μmol of GluNA hydrolyzed/min/mg of protein) means ± the standard error from three to six separate experiments with duplicate determinations.

Recombinant His-APAs	No Ca2+	4 mm Ca2+	Factor of stimulation
Wild type	1.98 ± 0.12	14.67 ± 0.42d	8
Ser-348	3.05 ± 0.15a	31.54 ± 1.33a,c	10
Asp-348	0.8 ± 0.05a	1.6 ± 0.14a,d	2
Tyr-348	0.25 ± 0.007b	7.4 ± 0.13a,d	30

^ap < 0.05 (corresponding mutated His-APA vs. corresponding wild-type APA)

^bp < 0.01 (corresponding mutated His-APA vs. corresponding wild-type APA)

^cNot significant when compared to the corresponding recombinant enzyme activity in the absence of Ca²⁺

^dp < 0.05