Table III.

The Effect of Metal Ions on Catalysis

	Before dialysis [kcat (s−1)] (1)	After dialysis [kcat (s−1)] (2)	After dialysis with metals [kcat (s−1)] (3)
wtTAP	50.04	0.46	30.44
H135D	101.5	15.6	105
H135E	146	1.28	117.6

Weakly bound metals were removed by extended dialysis in 20 mM Tris pH 7.6. AP activity toward the pNPP substrate was measured before treatment (1), after dialysis, and after loading the enzymes with 10 mM MgCl₂, and 1 mM ZnCl₂. k_cat values in (1) and (3) were determined in the same buffer as in Table II, whereas in (2), no metals were added. Reported values are the average of three measurements and standard deviations do not exceed 5%.