For immunoelectron microscopic localization of isopenicillin N synthase (IPNS), glutaraldehyde-fixed mycelium of Penicillium chrysogenum PQ-96 was dehydrated by progressive lowering of the temperature and embedded into Lowicryl K4M at -3 5°C . This procedure resulted in good structural preservation such that the method of on-section labelling using antibody to IPNS from Cephalosporium acremonium CO 278 with the indirect antibody-gold technique could be successfully applied. By this method IPNS was localized in vesicular compartments belonging probably to the Golgi body and in the cell wall.

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Excretion of exocellular DD-carboxypeptidases was tested using 128 strains of streptomycetes. Exocellular enzyme activity was shown in 13% of the strains investigated. Streptomyces strains showed low activity of excretion of DD-carboxypeptidases: 2.7-4.8 ~tM of released C-terminal D-alanine (D-AIa) 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 ~tM D-Ala/I culture supernatant per minute. The affinity of exocellular DD-carboxypeptidase of S. erythraea 64-575 for fl-lactam antibiotics was assessed by a statistical computer programme. The enzyme showed the lowest affinity for sodium cefotaxime, IDs0(M) = 7.5 × 10-6, and the highest for potassium cephalosporin C, IDs0(M)=5.0x 10 -9, IDs0(M) representing the molar concentration of fl-lactam antibiotics which decreased by 50% the release of D-Ala.

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