Proximal ligand

All successful myoglobin and hemoglobin model compounds provide steric bulk on the distal side of the porphyrin ring with a hydrophobic pocket for complexation of dioxygen as well as a bulky alkyl imidazole proximal ligand... 

Electrochemistry of Variants with an Altered Proximal Ligand... 

Evaluation of the contribution made by the proximal ligand to the oxidation-reduction equilibrium of Mb (H93 in the wild-type protein (Fig. 2)) has been more difficult because substitution of the proximal residue results in expression of apo-Mb without heme incorporation. All of the available data for these variants (Table I), therefore, derive from proteins prepared by reconstitution of purified recombinant apoprotein with exogenous heme 69, 70, 72). In those cases where trace quantities of native Mb are produced (73), heme extraction followed by reconstitution was undertaken to eliminate complications from suIfMb... 

Although more limited, sufficient spectroscopic data is available on the HO-2 isoform to confirm that the proximal ligand is also an imidazole. A 28-kDa catalytically active fragment of human HO-2 obtained by tryptic digestion of the enz5mie expressed in E. coli was shown by optical, resonance Raman, and EPR studies to have a neutral (imionized)... 

Mutation of His 132 to an alanine, glycine, or serine in the truncated human heme oxygenase, in accord with identification of His25 as the proximal ligand, does not alter the cpe-His band in the resonance Raman spectrum of the Fe deoxy protein (82). The mutations result in the formation of two separate fractions when the protein is expressed in... 

The reported data as far as Zn NMR is concerned are sporadic, and very limited due to difficulties from a technical point of view, the nature of the Zn nucleus, as well as all factors responsible for the latter such as concentration, the nature of the proximity ligands etc. A descriptive analysis of the last reported data concerning Zn NMR studies will be developed with respect to the role of Zn ion or element in materials science or bioinorganic chemistry in both solution and solid state. 

Tyrosine and histidine are proximal ligands of catalase and peroxidase, respectively. 

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