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The inhibiting activity of the cultural broth filtrate against phospholipase C was studied in 2920 actinomycetes. The inhibitor which did not bind to blood proteins was produced by 12 cultures. Streptomyces saraceticus, strain 0845, had the highest antiphospholipase activity. The activity was detected in the cultural broth of S. saraceticus by the first day of its growth and reached the maximum by the third day. Soybean flour and sucrose were shown to be the best sources of nitrogen and carbon for the manifestation of the inhibiting activity against phospholipase C. The culture responded to the level of aeration in the medium and the most intensive inhibitor synthesis was found at the oxygen solution rate of 0.84 to 1.32 g O2 per litre per hour. The inhibiting activity was preserved when the cultural broth filtrate was kept at room temperature and pH from 4.0 to 11.5 for 3 hours.

Streptoverticillium mycoheptinicum, a producer of the antifungal antibiotic mycoheptin, was found to produce an inhibitor of Clostridium perfringens phospholipase C. Dynamics of the enzyme accumulation in the culture liquid filtrate was studied. A technique was developed for purification of the inhibitor, which includes adsorption, selective precipitation, ultrafiltration, gel chromatography and isoelectric focusing. The inhibitor was found to be of the peptide nature with the molecular weight of 3500-4000 and to exist in two isoforms with the isoelectric points of 8.15 and 8.50.

Principles of detecting organisms producing beta-lactamase inhibitors among soil actinomycetes were developed. For detecting such cultures it was recommended to use the Gauze agarized medium No. 1 supplemented with beta-lactam antibiotics. Benzylpenicillin proved to be the most efficient. Various liquid fermentation media for detecting the inhibitory activity of soil actinomycetes were compared. Two media were the most favourable i.e. the glucose-yeast medium No. 18/3 and the soybean-glucose medium with Na2SO4 and CoCl2 No. 20/3. The use of test cultures with relatively low resistance to benzylpenicillin was shown expedient in screening cultures producing beta-lactamase inhibitors. Test cultures with high resistance should be used in more detailed characterization of the selected cultures.