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Indian Journal of Chemistry -Section B (IJC-B) >
IJC-B Vol.51B [2012] >
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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