Some kinetic and inhibition properties of deepwater pink shrimp from Aegean Sea: pH, temperature, kinetic and inhibition

Abstract

The aim of this study was to identify the tyrosinase activity in the extract of deepwater pink shrimp (Parapenaeus longirostris) using L-3,4- dihydroxyphenylalanine (L-DOPA) as a substrate. Therefore, some kinetic properties of polyphenol oxidase (PPO) from deepwater pink shrimp and the inhibitory effect of gallic acid and L-cysteine on its PPO activity were investigated. The enzyme showed maximal activity at pH 4.0 and 35 0 C. It was stable in a wide pH range of 3.0-6.5 but unstable at a temperature greater than 55 0 C. Kinetic constants were KM = 10 mM and Vmax = 10.000 EU/mL min. Gallic acid showed the mixed type reversible inhibition with a KI value of 0.96 mM, whereas Lcysteine exhibited the uncompetitive reversible inhibition with a KI value of 6.70 mM. Thus, gallic acid and L-cysteine could inhibit melanosis in deepwater pink shrimp with different modes of inhibition towards PPO