Effect of carob pod extract on cellulolysis, proteolysis, deamination, and protein biosynthesis in an artificial rumen. Appl. Microbiol. 13:437-442. 1965.-Carob pod extract and its tannin and sugar fractions were compared with gallotannic acid and sucrose for their effect on the cellulolytic, proteolytic, protein biosynthetic, and deaminative activities of rumen microorganisms. The inhibitory effects of carob pod extract upon the cellulolysis and deamination were correlated mainly with its sugar, rather than its tannin components. On the other hand, proteolytic activity and protein biosynthesis were more significantly affected by the tannin fraction. In contrast to the tannin fraction of carob pod extract, gallotannic acid inhibited cellulolytic activity. The harmful effect of a low concentration of tannins on protein biosynthesis could be prevented by the addition of carbohydrates to the reaction mixture. At high tannin concentration (40 jug/ml), however, the addition of carbohydrates did not prevent the inhibition.