On the mechanism of action of the antibiotic O-carbamyld-serine in Streptococcus faecalis.

Lynch, Judith L. (Northwestern University, Evanston, Ill.), and Francis C. Neuhaus. On the mechanism of action of the antibiotic O-carbamyl-d-serine in Streptococcus faecalis. J. Bacteriol. 91:449-460. 1966.-The antibiotic O-carbamyl-d-serine, an analogue of d-alanine, is an inhibitor of bacterial cell-wall biosynthesis. Growth of Streptococcus faecalis R in the presence of O-carbamyl-d-serine resulted in the accumulation of the cell-wall precursor uridine diphosphate-NAc-muramyl-l-alanyl-d-glutamyl-l- lysine (UDP-NAc-muramyl-l-ala-d-glu-l-lys). The incorporation of d-alanine from l-alanine into peptidoglycan is catalyzed by the sequential action of the following enzymes: (i) alanine racemase; (ii) d-alanine: d-alanine ligase [adenosine diphosphate (ADP)]; (iii) UDP-NAc-muramyl-l-ala-d-glu-l-lys: d-ala-d-ala ligase (ADP); (iv) phospho-NAc-muramyl-pentapeptide translocase [uridine monophosphate (UMP)]. O-carbamyl-d-serine is an effective inhibitor of the alanine recemase (K(i)= 4.8 x 10(-4)m, K(m) of l-alanine = 6.8 x 10(-3)m). In addition, d-ala-O-carbamyl-d-ser was formed when d-alanine and O-carbamyl-d-serine were incubated with d-alanine: d-alanine ligase (ADP). This dipeptide was utilized by the UDP-NAc-muramyl-l-ala-d-glu-l-lys: d-ala-d-ala ligase (ADP) with the formation of UDP-NAc-muramyl-l-ala-d-glu-l-lys-d-ala- O-carbamyl-d-ser. From a consideration of the following results, i.e., (i) accumulation of UDP-NAc-muramyl-l-ala-d-glu-l-lys; (ii) absence of d-ala-O-carbamyl-d-ser accumulation in bacterial cultures grown in the presence of O-carbamyl-d-serine; and (iii) effective inhibition of the racemase, it was concluded that the first enzyme, the racemase, is the primary site of antibiotic action.