Mm. Sojo et al., Oxidation of salsolinol by banana pulp polyphenol oxidase and its kinetic synergism with dopamine, J AGR FOOD, 48(11), 2000, pp. 5543-5547
Salsolinol, a tethrahydroisoquinoline present in banana and biosynthesized
from dopamine, was oxidized by banana pulp polyphenol oxidase to its corres
ponding salsolinol-o-quinone. This oxidation was pH-dependent and showed a
maximum at acidic pH values. At physiological pH of 5.0, the values obtaine
d for the kinetic parameter (V-m and K-m) were 62.5 muM/min and 1.7 mM, res
pectively. When dopamine was added to the reaction medium to imitate physio
logical conditions, salsolinol was co-oxidized by dopamine-quinone. When th
is phenomenon was studied oxygraphically, an unexpected activation of dopam
ine oxidation was found in the presence of salsolinol. This activation was
related with the enzyme's kinetic mechanism and was named "kinetic synergis
m", because a bad substrate activated a good one. A possible physiological
role is discussed.