Excretion of exocellular dd-carboxypeptidases was tested using 128 strains of streptomycetes. Exocellular enzyme activity was shown in 13% of the trains investigated. Streptomyces strains showed low activity of excretion of dd-carboxypeptidases: 2.7-4.8 μM of released C-terminal d-alanine (d-Ala) residue/1 culture supernatant per minute. Saccharopolyspora erythraea mutants produced considerably higher levels of exocellular enzymes, the dynamics of excretion depending upon the medium used. The highest activity of exocellular dd-carboxypeptidase production was 44 μM d-Ala/1 culture supernatant per minute. The affinity of exocellular dd-carboxypeptidase of S. erythraea 64-575 for β-lactam antibiotics was assessed by a statistical computer programme. The enzyme showed the lowest affinity for sodium cefotaxime, ID 50 (M) = 7.5 × 10 -6 , and the highest for potassium cephalosporin C, ID 50 (M) = 5.0 × 10 -9 , ID 50 (M) representing the molar concentration of β-lactan antibiotics which decreased by 50% the release of d-Ala. © 1990 Springer-Verlag.
