The Inactivation of Invertase by Tyrosinase

Abstract

0.5 ml. of tyrosinase was incubated with 0.1 ml. of diluted invertase, 0.5 ml. of [image]/20 phosphate buffer at pH 6 and 0.5 ml. of water plus toluene for 18 hrs. at 37 C. In controls, the tyrosinase was inactivated by boiling. The residual activity of the invertase was measured. The samples were diluted to 5 ml. with buffer and at zero time were mixed with 5 ml. of 12% sucrose. One ml. samples were removed at given times and added to 3 ml. of dinitrosalicylic acid reagent for reducing sugars. The intensity of color after heating the solns. was measured with the Coleman Universal Spectrophotometer and converted to mg. of invert sugar. The liberation of invert sugar from sucrose by invertase followed zero order kinetics during the initial phase of the hydrolysis. The invertase oxidized by active tyrosinase was only 50% of the activity of the control invertase which was treated with boiled tyrosinase. Invertase in over 100 expts. was inactivated 10-40% when compared with the control invertase. Crude tyrosinase did not inactivate invertase, and purified tyrosinase of high "catecholase" activity was very effective. It was probable that invertase was inactivated directly rather than by a high-molecular wt. impurity. Invertase was partially inactivated by incubation with mushroom tyrosinase. Inactivation was best explained on the basis of an oxidation of essential tyrosyl groups in the invertase molecule by tyrosinase.