His imidazole

Natural a-amino acids provide a moderately effective N,OJ chelating donor set derived from carboxylate and amino groups, respectively. Several side-chain donor atoms may also be involved in metal ion coordination, especially those of Cys (thiol sulfur) and His (imidazole nitrogen(s)). (Abbreviations for amino acid residues are those recommended by IUPAC-IUB.1702)... 

Since both proteins bound at pH 7.4, the result suggests that both had isoelectric point (pi) values <7.4. Furthermore, the 78.8-kDa protein bound to the IMAC spot, while the 14.9-kDa protein did not bind. This suggests that the 78.8-kDA protein had a free His imidazole group on its surface, while the 14.9-kDa protein did not have an available metal binding domain. 

His imidazole ring NH hydrogen atoms at the interfaces between helix and loop regions in myoglobin... 

Observation of high-frequency shifted His imidazole ring NH proton signals... 

The high-frequency shifted His imidazole ring NH proton signals in a variety of oxidation/ligation states of Mb are compared in Fig. 16. Observations of... 

NOE connectivities provided the shifts of non-exchangeable proton signals of these His imidazole rings. Their shifts are summarized in Table 2. The similarity in the shifts between metMb(OH ) and diamagnetic Mbs, i.e. Mb(CO) and oxy-Mb (MblO )), demonstrates that paramagnetic contribution to these resonances is quite small. Semiquantitative analysis of 6pc, due to... 

Furthermore, the pH dependence of the high-frequency shifted His imidazole NH proton signals of apoMb are essentially similar to those of the corresponding signals of metMb(OH ) (see Fig. 12), except that the pH value... 

Structural characterization of the interfaces from analysis of the high-frequency shifted His imidazole ring NH proton signals has revealed that there is a path for the transmission of structural information between the heme active site and the EF—H interface. The presence of a similar structural correlation between the heme active site and the EF—H interface has been... 

Fig. 34. (A) pH dependence of high-frequency shifted His imidazole NH proton signals of human SOD in 90%H2O/10% H2O at 25 °C. (B) pH profiles of the enzyme activity (upper) and His 43 NgH proton shift (lower). The pH-dependent His 43 NgH proton shift exhibits a pAa value of 10.7. -...

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