PRODUCTION OF L-DOPA FROM TYROSINASE IMMOBILIZED ON NYLON-6,6 - ENZYME STABILITY AND SCALEUP

The production of L-3,4 dihydroxyphenylalanine (L-DOPA) from mushroom tyrosinase immobilized on chemically modified nylon 6,6 membranes was investigated in a batch reactor. The effects of product inhibition, ox ygen partial pressure, and scaleup upon L-DOPA production rates and ty rosinase activity were studied L-DOPA production rates were strongly i nfluenced by oxygen and L-DOPA concentrations. Kinetic modeling reveal ed that L-DOPA concentrations as low as 1 mM would reduce the L-DOPA p roduction rate by approximately 50% due to competitive inhibition. The average L-DOPA production rate increased by 10% when the oxygen parti al pressure was increased from 21 kPa and 100 kPa; however, at higher oxygen partial pressures (50 kPa and 100 kPa), the rare of oxidative i nactivation of tyrosinase increased causing the enzyme half-life to de crease from 46 h under 21 kPa oxygen to 7.7 h under 100 kPa oxygen. Th e turnover number was approximately 1,170 under 21 kPa oxygen, but dro pped to approximately 150 under 100 kPa oxygen. Scaleup from a 500-ml batch reactor to 1-l and 2-l reactors proved to be straightforward. Es sentially identical production rates were obtained as long as the enzy me concentration within the reactor was held constant. If the enzyme c oncentration was varied, a proportional change in the L-DOPA productio n rate was not observed due to the effects of product inhibition. (C) 1998 Elsevier Science Inc.