TABLE 2.

Relative activity of HMG/CHA aldolase with various metal ions

Activity obtained with MgCl₂ (0.11 mmol·mg⁻¹·min⁻¹) is taken as 100%. Assays, with the exception of Zn²⁺ and Cu²⁺, were performed with 2.2 μg of aldolase, 10 mm HMG, 1.0 mm of the respective metal chloride salts, 0.3 mm NADH, 30 units of LDH, and 100 mm sodium HEPES buffer, pH 8.0, in a total volume of 1 ml. Activity with Zn²⁺ and Cu²⁺ was determined by the discontinuous method (8). For assays with Zn²⁺, a high spontaneous aldol cleavage rate in the presence of 1.0 mm ZnCl₂ necessitates that 0.1 mm ZnCl₂ be used instead. ND, no activity was detected above the detection limit of 10 nmol·min⁻¹·mg⁻¹ protein.

Metal ion	Relative activity
	%
Mg2+	100.0 ± 2.8
Mn2+	90.3 ± 5.7
Co2+	64.7 ± 3.6
Ni2+	28.2 ± 3.4
Cd2+	5.0 ± 0.2
Zn2+	49.6 ± 2.7
Cu2+	ND
Ca2+	ND
EDTA	ND