Table 2.

Mg²⁺ requirement for SPP activity

Additions	Activity, μmol min−1 ml−1
8 mM MgCl2*	2.95
None	0.34
13 mM EDTA	0.01
1 mM MgCl2	2.96
1 mM MgCl2 + 13 mM EDTA	0.05
0.1 mM MgCl2	2.80
0.01 mM MgCl2	1.61
0.002 mM MgCl2	0.75

Purified SPP was desalted by passage through a Sephadex G-25 column equilibrated with 25 mM Hepes-K⁺, pH 7.0, and assayed for activity with 1.2 mM Suc6P and various concentrations of MgCl₂ or EDTA as shown. 

^*Enzyme before desalting on Sephadex G-25.