TIME-DEPENDENT INHIBITION OF GRAPE POLYPHENOL OXIDASE BY TROPOLONE

A kinetic study of inhibition of the catecholase activity of grape polyphenol oxidase by tropolone has been made. The results obtained showed that tropolone inhibits grape polyphenol oxidase in a non-classical manner. A decrease in initial velocity to a steady-state inhibited velocity can be observed on a time scale of minutes. The time dependence, which is unaltered by prior incubation of the enzyme with the inhibitor, is consistent with a first-order transition. Kinetic data obtained correspond to those for a postulated mechanism that involves rapid formation of an enzyme-inhibitor complex that subsequently undergoes a relatively slow reversible reaction, since inhibition was reversed by the addition of CuSO4 to the reaction medium. Likewise, kinetic parameters characterizing this type of inhibition have been evaluated by means of nonlinear regression of product accumulation curves.