title: Reduction of ferrylmyoglobin by theanine and green tea catechins. Importance of specific Acid catalysis.
abstract: Reduction of the hypervalent heme pigment ferrylmyoglobin by green tea catechins in aqueous solution of pH = 7.5 was investigated by stopped-flow spectroscopy. Reduction by the gallic acid esters epigallocatechin gallate (EGCG, k2 = 1460 L mol(-1) s(-1), 25.0 °C, 0.16 ionic strength) and epicatechin gallate (ECG, 1410 L mol(-1) s(-1)) was found faster than for epicatechin (EC, 300 L mol(-1) s(-1)) and epigallocatechin (EGC, 200 L mol(-1) s(-1)), even though the gallate ion (G, 330 L mol(-1) s(-1)) is similar in rate to EC. The rate for reduction by EC, EGC, ECG, EGCG, and G shows no correlation with their oxidation potentials or phenolic hydrogen-oxygen bond dissociation energy, but with the pKa of the most acidic phenol group. Theanine, with an acidity similar to that of EC, reduces ferrylmyoglobin with a similar rate (200 L mol(-1) s(-1)), in support of general acid catalysis with an initial proton transfer prior to electron transfer.
authors: Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors: Jie
authors: J
authors: Yin
authors: Mogens L
authors: ML
authors: Andersen
authors: Leif H
authors: LH
authors: Skibsted
mesh_terms: D002384:Catalysis; D002392:Catechin / Q000031:analogs & derivatives / Q000737:chemistry*; D055598:Chemical Phenomena; D005707:Gallic Acid / Q000737:chemistry; D005971:Glutamates / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008786:Metmyoglobin / Q000737:chemistry*; D010084:Oxidation-Reduction; D013662:Tea / Q000737:chemistry*
chemical_list: D005971:Glutamates; D013662:Tea; C028048:ferrylmyoglobin; D008786:Metmyoglobin; D005707:Gallic Acid; C026166:theanine; D002392:Catechin; C062669:epicatechin gallate; C045651:epigallocatechin gallate