N-Acetylmuramoyl-l-alanine amidase

This chapter describes the activity, specificity and structural chemistry of N-Acetylmuramoyl-l-alanine amidase. N-Acetylmuramoyl-l-alanine amidases are peptidoglycan hydrolases with the specificity to cleave the amide bond between the lactyl group of the muramic acid and the α-amino group of l-alanine, and are able to cause dissolution of the peptidoglycan structure and thus do not exhibit peptidase activity. Most amidases are able to act on intact cell wall peptidoglycan, either associated with living bacteria or as isolated peptidoglycan, resulting in a loss of absorbance by the insoluble substrate. A general assay for peptidoglycan hydrolases by zymogram activity has been developed. The assay for amidase activity is the hydrolysis of peptidoglycan substrate followed by the identification of new l-alanine N-termini. The amidases show varying substrate specificities and biochemical properties. The LytA autolytic amidase of Streptococcus pneumoniae requires cell walls containing choline for activity. Both the autolysin LytC and the cryptic prophage lytic enzyme CwlA of Bacillus subtilis are able to hydrolyze purified peptidoglycan, although they have a higher specific activity on cell wall peptidoglycan containing teichoic acids.