Inhibition of Diphenol Oxidase Activity of Strawberry (Fragaria Sp) Using L-Cysteine and L-Glycine

L-glycine and L-cysteine exhibit, strong inhibition of partial purified DIPHENOL OXIDASE at strawberry. The concentration of L-glycine inhibiting Diphenol oxidase activity by 50% (IC50) was 0.5 and 0.4 mM at pH 6.7 and 8, respectively. The inhibition of partial purified Diphenol oxidase activity is pH and inhibitor dependent. Kinetic studies indicate that L-glycine is a uncompetetive inhibitor and L-cysteine is competitive and noncompetitive inhibitor of Diphenol oxidase activity. Vmax and Km for catechol oxidation at pH 6.7 and in presence of L-glycine (1.4M) was 0.09 ∆A min-1 and 10 mM. Vmax for catechol oxidation at pH 8 and in absence of L-glycine was 0.09 ∆A min–1, with a Km of 3.5 mM. Kinetics parameters indicated the highest catalytic efficiency ( units mg–1 prot mM–1) with catechol and L-glycine at pH 8: 4 , then with L-cystein at pH 8: 1.7, L-glycine at pH 6.7: 1.4 and L-cystein at pH 6.7: 0.25.