In vitro enzyme kinetics of microencapsulated tyrosinase

In this study, we prepared microencapsulated tyrosinase and studied its enzyme kinetics and its stability at different pH and temperature. The Km for both free and microencapsulated tyrosinase is 465 microM. The Vmax for the microencapsulated tyrosinase is 49.02 mg/dl x min, whereas that of tyrosinase in free solution is 114.95 mg/dl x min. At the extreme pH of pH 2 and pH 10, free tyrosinase lost all its enzyme activity, whereas microencapsulated tyrosinase retained 14% of its original activity at pH 2 and 17% of its original activity at pH 10. Further in vitro studies were carried out to study the pH optimum of the microencapsulated enzyme at different pH values corresponding to those along the gastrointestinal tract. In temperature stability studies at 4 degrees C and 37 degrees C, higher enzyme activity remained in microencapsulated tyrosinase solution than that of free enzyme solution. Therefore, our results show that microencapsulated tyrosinase is significantly more stable than free tyrosinase. In subsequent studies, we show that daily oral administration of microencapsulated tyrosinase significantly lowers systemic tyrosinase after 3 days and maintains this low level as long as oral administration continues. When combined with one intravenous injection of polyhemoglobin-tyrosinase, the systemic tyrosine level can be lowered within one hour.