Table 1.

Sedimentation equilibrium ultracentrifugation analysis of CzrA and NmtR

Sample, 5 μM	Model	Molarmass, g/mol	Kdimer,×105 M−1*	χ2, ×10−5†
apo-CzrA‡	Single, ideal¶	19307		4.66
	Dissociable dimer‖	11975	1.7 (±0.3)	4.59
Co(II)1-CzrA§	Single, ideal	20358		5.42
	Dissociable dimer	11851	4.8 (±0.1)	5.56
Ni(II)1-CzrA§	Single, ideal	20126		4.71
	Dissociable dimer	12051	6.3 (±0.2)	5.34
Zn(II)1-CzrA§	Single, ideal	19784		4.85
	Dissociable dimer	11858	4.5 (±0.2)	5.21
apo-NmtR‡	Single, ideal	20069		4.57
	Dissociable dimer	12549	1.9 (±0.4)	5.83
Co(II)1-NmtR§	Single, ideal	21952		5.96
	Dissociable dimer	12849	3.9 (±0.4)	7.56
Ni(II)1-NmtR§	Single, ideal	21539		5.45
	Dissociable dimer	12877	4.1 (±0.4)	6.22
Zn(II)1-NmtR§	Single, ideal	19359		5.41
	Dissociable dimer	12597	3.7 (±0.6)	6.96

^*The association constant as estimated with a monomer–dimer equilibrium model (model 2). 

^† x² = (∑[f(X_i − Y_i)]²/N − n), where N is the number of observations, n is the number of fitting parameters, f( ) is the fitting function, X_i and Y_i are data points, and N − n equals the degrees of freedom. 

^‡ Conditions: 10 mM Hepes, 0.40 M NaCl, 0.1 mM EDTA, pH 7.0; 25°C. 

^§ Conditions: 10 mM Hepes, 0.40 M NaCl, pH 7.0; 25°C. 

^¶ Model 1 fits the data to a single, ideal species with calculated dimer molecular weights of 23,715 g/mol for CzrA and 25,409 g/mol for NmtR (see Materials and Methods). 

^‖ Model 2 fits the data to a reversible associating system assuming a monomer-dimer equilibrium. The calculated monomer molar masses are 11,857 g/mol for CzrA and 12,704 g/mol for NmtR (see Materials and Methods).