THE MECHANISM OF ACTION OF DD-PEPTIDASES - THE ROLE OF TYROSINE-159 IN THE STREPTOMYCES R61 DD-PEPTIDASE

Tyrosine-159 of the Streptomyces R61 penicillin-sensitive DD-peptidase was replaced by serine or phenylalanine. The second mutation yielded a very poorly active protein whose rate of penicillin binding was also drastically decreased, except for the reactions with nitrocefin and m ethicillin. The consequences of the first mutation were more surprisin g, since a large proportion of the thiolesterase activity was retained , together with the penicillin-binding capacity. Conversely, the pepti dase properties was severely affected. In both cases, a drastic decrea se in the transferase activity was observed. The results are compared with those obtained by mutation of the corresponding residue in the cl ass A beta-lactamase of Streptomyces albus G.