Juana Cabanes

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A kinetic study of the diphenolase activity of latent polyphenol oxidase (PPO), purified from Iceberg lettuce (Lactuca sativa L), revealed a sigmoid relationship between the reaction rate and the substrate concentration with a high Hill coefficient (n(H) = 3.8). This positive cooperativity had not been previously described for any PPO. Furthermore, the(More)
This paper describes a simple continuous spectrophotometric method for assaying phospholipase A(2) (PLA(2)) activity. The procedure is based on a coupled enzymatic assay, using dilinoleoyl phosphatidylcholine as phospholipase substrate and lipoxygenase as coupling enzyme. The linoleic acid released by phospholipase was oxidized by lipoxygenase and then(More)
This paper analyzes the kinetic and structural characteristics of polyphenol oxidase (PPO) from peach cv. Catherina. The PPO was obtained in a latent state in both the soluble and membrane-bound forms, and both forms were activated by acid shock and the detergent SDS. Plant defense is the main function assigned to PPO, which would be activated by the acid(More)
It was found that kojic acid, which is used in cosmetics for its excellent whitening effect, inhibits catecholase activity of tyrosinase in a non-classical manner. A decrease in the initial velocity to a steady-state inhibited velocity can be observed over a few minutes. This time-dependence, which is unaltered by prior incubation of the enzyme with the(More)
A kinetic study of the activity of soluble and membrane-bound latent polyphenol oxidase (PPO) extracted from beet root (Beta vulgaris) was carried out. For the first time, two types of behavior (hyperbolic and sigmoid) are reported in the same enzyme for PPO activation by the surfactant sodium dodecyl sulfate (SDS), depending on substrate nature. A kinetic(More)
Polyphenol oxidase (PPO) was extracted from beet root, in both soluble and membrane fractions, and in both cases the enzyme was in a latent state. PPO from the membrane fraction showed no diphenolase activity unless it was activated by trypsin or sodium dodecyl sulfate (SDS). The kinetics of the activation process of latent PPO by trypsin was studied and(More)
Polyphenol oxidase from iceberg lettuce (Lactuca sativa L.) chloroplasts was released from the thylakoid-membrane by sonication, and it was extensively purified to homogeneity as judged by SDS-PAGE. Purification was achieved by ammonium sulfate fractionation, gel-filtration chromatography, and ion-exchange chromatography. Two molecular forms were separated(More)
In the pathway of melanin biosynthesis originating from L-tyrosine, the dopachrome accumulation at physiological pH is produced with a pronounced lag period, during which the level of L-dopa increases, following a sigmoidal kinetics to reach a steady-state. A kinetic model has been proposed for the overall pathway of melanization from L-tyrosine to(More)
Patatin is a family of glycoproteins that accounts for 30–40% of the total soluble protein in potato (Solanum tuberosum L.) tubers. This protein has been reported to serve as a storage protein and also to exhibit lipid phospholipase activity. This paper describes a simple continuous spectrophotometric method for assaying patatin phospholipase activity. The(More)