Effects of Overall Structure on Activity 8-3 Mutant

The MCD spectrum of Seri 27Ala mutant GpdQ showed that the enzyme was able to assemble a dinuclear Co(II)Co(II) active site in the absence of substrate (to a certain extent, 40 % of the P-sites assembled). Serl27 forms a hydrogen bond to AsnSO which is responsible for the enzyme being a mononuclear enzyme in the 

3 Understanding the Overall Structure of GpdQ and Metal Binding 

3 Binding of Different Metals to the pSite of Fe(II) Half-apo GpdQ 

Metal ion association constants Kassoc (Kassoc = in the various Fe(II)-M(II) derivatives of GpdQ (M = Co, Mn, Zn, Cd) were determined at various pH values. A bell-shaped pH dependence was observed for the Fe(II)Zn(II), Fe(II)-Co(II) and Fe(II)Mn(II) derivatives, which indicates that (at least) two ionisable residues (characterized by pKai and pKa2) in the enzyme contribute to binding of metal ions. An overview of the pKa values of amino acid residues near the active site in GpdQ is shown in Table 3.6. 

The data were fitted to an equation derived for a diprotic system (Eq. 2.4, Chap. 2) [26]. For the Cd(II) derivative pKa2 is absent. pKai is in the range of 6. 

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