Biological Systems Metalloproteins and Related Model Compounds

Biological Systems Metalloproteins and Related Model Compounds 

In addition to a number of simple inorganic compounds. Sham and Wu examined anhydrous Zn(CFl3COO)2, Zn[ImH]4(C104)2 (ImH = imidazole) and Zn[SC(NH2)2]4(N03)2, which represent Zn04, ZnN4 and ZnS4 tetrahedral coordination environments in enzymes [24]. Their MAS spectra are shown in Fig. 1.2. The Cq values of these compounds are fairly small (less than 3.5 MFIz). Zn formate dihydrate and Zn acetate dihydrate represent 

Zn centre are cis to each other and the remaining two positions are occupied by water molecules. Zn EFG parameters were determined first by Oldfield and co-workers [25], Vosegaard et al. [26] and Larsen et al. [27]. 

The very first direct observation of a Zn in a metalloprotein was reported in 2001 [48]. Using Zn-enriched sample, Zn static spectrum of the minimal DNA-binding domain of xeroderma pigmentosum A (XPA-MBD), a 14.7 kDa protein, was observed at 25 K by CP/QCPMG method at 9.4 T. The local Zn environment was found to be similar to that of Zn[SC (NH2)2]4(N03)2, a model compound, su esting a sulphur coordination. 

The same group further investigated human carbonic anhydrase isozyme II (hCAII), which is a 30 kDa protein [53]. The Zn ion is tetrahedraUy bound to the imidazole side chains of three histidines. The fourth Hgand can be either water or hydroxide. It was believed at the time that the nature of the fourth ligand would depend on pH value. If the argument were accepted, the Zn spectra of hCAII at pH 5 and 8.5 would look drastically different since the theoretical calculations of the EFG tensor based on the 

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