Abstract
Berberine inhibits the tyrosine decarboxylase activity of Streptococcus faecalis if the enzyme preparation is preincubated with the alkaloid under slightly alkaline conditions prior to initiation of the enzyme reaction at its optimum pH(5.5). When the preincubation is carried out at acidic pH, berberine causes no inhibition. At the pH range from 7.0 to 7.4 the enzyme can be protected from the inhibitory action of berberine by conducting the preincubation in the presence of a large amount of pyridoxal phosphate. This fact suggests that berberine competes with pyridoxal phosphate for the apoenzyme at least at this pH range. At pH 8.0, however, no protection can be observed even if the preincubation mixture contains an excess of pyridoxal phosphate, the reason for which is as yet to be explored. The possibility that the competition between berberine and pyridoxal phosphate is, at least partly, responsible for the bacteriostatic action of the alkaloid is discussed.
