Streptococcus mutans is responsible for causing
dental caries in humans and utilizes
sucrose for its growth. The
dextransucrase (EC 2.4.1.5) is responsible for
sucrose metabolism, which exhibits both hydrolytic and
glucosyltransferase activities. In this study, we examined the effects of the plant
phenols, namely gallic, tannic and syringic
acids and aqueous extracts of certain traditionally used chewing sticks (Acacia arabica, Azadirachta indica, Pongamia pinnata and Salvadora persica) for prevention of
dental caries on hydrolytic activity of dextransucrsae in S. mutans.
Gallic acid (4-5 mM) produced 80-90% inhibition of the
enzyme, while
tannic acid (0.2 mM) and
syringic acid (5 mM) inhibited the
enzyme activity 80% and 48%, respectively in vitro. The aqueous extracts of chewing sticks produced 35-40% inhibition of
dextransucrase activity at 5 mg
phenol concentration. Kinetic analysis revealed mixed-type of
enzyme inhibition by
polyphenols, where both K(m) and V(max) were altered. The value of K(i) for tannic, gallic and syringic
acids were 0.35, 1.6 and 1.94 mM, respectively. The
enzyme inhibition by
polyphenols was optimum at pH 7-7.5, while by
plant extract was maximum at pH 5-6. These results suggest that plant
polyphenols may find potential applications in the prevention and control of
dental caries by inhibiting
dextransucrase activity in S. mutans.