Extracts of certain strains of Actinobacillus actinomycetemcomitans are inhibitory to strains of Streptococcus sanguis such as S. sanguis ATCC 10556. The isolation of a protein from an A. actinomycetemcomitans sonic extract which copurified with the inhibitory activity was accomplished by preparative isoelectric focusing, Sephadex G-100 gel filtration chromatography, and preparative polyacrylamide gel electrophoresis (PAGE). The resulting isolated protein, which focused at a pH of 6.1 to 6.3, appeared as a single band in anionic nondissociating PAGE analysis. This protein could be dissociated into two subunits with molecular weights of 50,000 and 70,000, which were resolvable by PAGE analysis. A 1,758-fold increase in specific activity was seen in the purified inhibitory protein compared with the crude sonic extract starting material. The properties of the inhibitory activity in the A. actinomycetemcomitans extract are characteristic of a bacteriocin. Accordingly, we propose the name actinobacillicin for the inhibitory protein.
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