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IJC-B Vol.51B(08) [August 2012] >


Title: Protective role of native bovine serum albumin and alpha-unsaturated fatty acids on catechin oxidation
Authors: Mitra, Sankar P
Keywords: Catechin
Polyphenols
Ascorbic acid
UV Oxidation
Singlet oxygen
Free radicals
Reactive oxygen species
BSA
Kinetics
UV-Vis spectra
Michaelis constant
Lineweaver-Burke plot
Arrhenius equation
Issue Date: Aug-2012
Publisher: NISCAIR-CSIR, India
Abstract: Catechin, a common ingredient of tea and coffee is a colourless water soluble compound which undergoes spontaneous oxidation by aerial O2, heat and also by UV exposure or ammonium persulfate (APS) treatment resulting in a noticeable change to yellow colouration (λmax = 440 nm). Several α-unsaturated fatty acids (ascorbic, maleic, sorbic but not acrylic), β-mercapto ethanol (BME) and native bovine serum albumin (BSA) block the colouring process whereas the alkylated BSA fails to do so, confirming the reducing role of thiol (–SH) group(s) within the protein molecule. But alkylation does not change either the affinity (Kd) or the capacity (Bmax) of catechin binding at pH 7.5 (Kd ~ 0.8 nM and Bmax ~ 4.0 mol/mol BSA). Interestingly, a large increment in Bmax is observed at pH 4.5. Additionally, the native BSA acts as a non-competitive inhibitor during oxidation of catechin as analyzed by the Lineweaver-Burke plot. The oxidation by APS follows the Michaelis equation and the rate (Vmax) is favourable at pH 8.5 (order → pH: 8.5 > 7.5 > 10.5) whereas the activation energy (∆E) deduced from Arrhenius equation shows that the reaction is favourable at higher pH. These incidents insist to hypothesize that APS, UV illumination and aerial oxygenation produce the same yellow poly-phenolic species as proven by the identical spectral changes associated with any of these procedures. The reducing agents interfere by blocking the crucial oxidative pathway.
Page(s): 1131-1144
CC License:  CC Attribution-Noncommercial-No Derivative Works 2.5 India
ISSN: 0975-0983(Online); 0376-4699(Print)
Source:IJC-B Vol.51B(08) [August 2012]

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