Azurin spectral characteristics

It is notable that Cu(NH3)3(SH)", which is a simple model of the type 1.5 Metl21-His azurin mutant has (p = 53-54°. Most probably, the spectral characteristics of the type 1.5 proteins are an effect both of the flattened tetragonal structure and the presence of a fourth strong ligand (in type 1.5 proteins the weak methionine ligand is replaced by a stronger ligand). 

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