3.4.22.52	Ca2+	half-maximal activity at 0.04 mM, maximal activity at 0.1 mM	643967	
3.4.22.52	Mn2+	synergistic acivation in combination with Ca2+	643967	
3.4.22.52	Sr2+	synergistic acivation in combination with Ca2+	643967	
3.4.22.52	Ca2+	Kd-value: 0.025 mM. 25% of the difference in Kd values between mu- and m-calpain can be ascribed to the N-terminal peptide of the large subunit, whereas the C-terminal EF-hand-containing domain IV accounts for 65% of the difference	643968	
3.4.22.52	Ca2+	the primary event in Ca2+-activation corresponds to the binding of Ca2+ to eight interacting sites, of which are four in each of the two calpain subunits. Progressive binding of the metal iuon is linearly correlated with the dissociation of the proteinase, which reaches completion when all eight binding sites are occupied. The affinity for Ca2+ in the native heterodimeric calpain is increased 2fold in the isolated 80000 Da catalytic subunit, but it reaches a Kd-value consistent with the physiological concentration of Ca2+ only in the active autoproteolytically derived 75000 Da form. Binding of the Ca2+ in physiological conditions, and thus the formation of the 75000 Da subunit, can occur only in the presence of positive modulators, the natural activator protein or highly digestible substrates. As a result, both dissociation into the constituent subunits and the autoproteolytic conversion of the native 80000 Da subunit into the active 75000 Da subunit form can occur within the physiological fluctuations in Ca2+ concentrations	643975	
3.4.22.52	Ca2+	requires 0.053 mM Ca2+ for half-maximal activity. Activation by Ca2+ promotes the separation of the two subunits of the expressed recombinant protein	643976	
3.4.22.52	Ca2+	half-maximal activation at 0.04 mM	643977	
3.4.22.52	Ca2+	half-maximal activity at 0.02 mM, maximal activity at 0.1 mM	643979	
3.4.22.52	Mn2+	0.1 mM, less than 10% as active as Ca2+	643979	
3.4.22.52	Sr2+	0.1 mM, less than 10% as active as Ca2+	643979