[The effect of point amino acid substitutions on the stability of phage T4 lysozyme. I. Asn101---Asp substitution].

The amino acid replacement Asn101-->Asp in the T4 phage lysozyme was obtained by site-directed mutagenesis and the plasmid mutant protein expression was constructed. Though the mutant protein circular dichroism (CD) spectrum is virtually unchanged as compared with the wild type protein and the enzymatic activity is 90% of that of the wild type protein, the stability of this mutant to urea-induced unfolding decreases and two stages in the denaturation process are observed.