The effect of amino acid analogues on alkaline phosphatase. Formation in Escherichia coli K-12. II. Replacement of tryptophan by azatryptophan and by tryptazan.

Several amino acid analogues may be incorporated into bacterial protein in place of the naturally occurring amino acid. These analogues cause the formation of nonfunctional enzymes and inhibit bacterial growth. Not all enzymes will be inactivated to the same extent, and the effect of an analogue on the activity of a particular enzyme should provide information on the essentiality of the natural amino acid to the function of the protein. Previous studies on the effect of histidine analogues on the formation of alkaline phosphatase from Escherichiu co& have shown that substitution of 1,2,4-triazole-3-alanine for histidine prevents formation of active enzyme (1). We have now investigated how the replacement of tryptophan either by 7-azatryptophan or by tryptazan (cY-amino-P-3-(indazole)propionic acid) affects this enzyme. Both of these tryptophan analogues are incorporated into bacterial protein and inhibit bacterial growth (2-4) ; however, they allow the formation of active alkaline phosphatase. Their substitution for tryptophan has relatively little effect on the structure and function of the enzyme. The main consequence of inserting azatryptophan or tryptazan into the polypeptide chain is seen in the ultraviolet absorbance and fluorescent spectra of the respective proteins.