39D-15

M. E. JARAMILLO-FLORES, Depto. Graduados Inv. Alimentos, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Carpio y Plan de Ayala, Mexico, DF, CP. 11340, Mexico, M. D. L. A. Hernández y Hernández, Instituto Andaluz de Ciencias de la Tierra, CSIC-Granada University, Campus Universitario Fuentenueva, Granada, 18002, Spain, and H. Hernández-Sánchez.

Justification: Enzymatic browning by polyphenol oxidase (PPO) in some fresh fruits and vegetables is important in food technology since it leads to major economic losses and low acceptance. Objective: To isolate and partially characterize the polyphenol oxidase from grapes from the Mexican San Emilion variety. Methods: The isolation of the PPO from this white variety was done using ammonium sulfate fractionation, gel chromatography (Sephadex G-75), ion exchange chromatography (Econo-pac High Q column). The partial characterization included molecular weight, isoelectric point, optimal activity temperature and pH, Km and V_max determinations. Catechol and 4-methyl-catechol were used as substrates. Results: The enzyme had a molecular weight of 36 kDa and an estimated pI of 5.9. The maximum activity was found around pH 6-6.5. The plot of activity vs temperature showed a maximum value at 30°C. Using a Lineweaver-Burk plot, the apparent Km and V_max values for catechol and 4-methyl-catechol were 31.85, 10.6 mM and 38.5 and 23.4 A.U. respectively. Significance: This work can be useful for future investigations focused on PPO crystallization and 3-D structure determination by NMR or X-ray Crystallography.