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Kinetic investigations of sulfite addition to flavanols.

ABSTRACT: Flavanols are an important class of natural products occurring in almost all plants, fruits and vegetables; they have a great influence on wine ageing potential, astringency, colour stability and biological activities. In wine, flavanols react with sulfur dioxide ([Formula: see text]), the most widely used preservative in oenology, leading to sulfonated products. Here we report a kinetic investigation, through LC-MS quantitative measurements carried out at different pH (3 and 4) and temperature values (23, 30, 40, 50 and [Formula: see text]), of the reaction products obtained by [Formula: see text] addition to both monomeric (epicatechin and catechin) and dimeric flavanols (procyanidin B2 and procyanidin B3). The results proved that: (a) the major sulfonation route that leads quickly and in good yields to monomeric 4[Formula: see text]-sulfonated derivatives passes through the acid-catalysed depolymerisation of proanthocyanidins; (b) monomeric flavanols lead to the same 4[Formula: see text]-sulfonated products, although in a considerably slower manner, and also to other sulfonated regioisomers; (c) the kinetic data in our hands, in particular the temperature dependence of the observed rates, suggest the involvement of two completely different reaction mechanisms for the [Formula: see text] addition to dimeric and monomeric flavanol substrates; (d) direct sulfonation of epicatechin is slightly faster than that of catechin.

SUBMITTER: Bonaldo F

PROVIDER: S-EPMC7393157 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Kinetic investigations of sulfite addition to flavanols.

Bonaldo Federico F Guella Graziano G Mattivi Fulvio F Catorci Daniele D Arapitsas Panagiotis P

Scientific reports 20200730 1

Flavanols are an important class of natural products occurring in almost all plants, fruits and vegetables; they have a great influence on wine ageing potential, astringency, colour stability and biological activities. In wine, flavanols react with sulfur dioxide ([Formula: see text]), the most widely used preservative in oenology, leading to sulfonated products. Here we report a kinetic investigation, through LC-MS quantitative measurements carried out at different pH (3 and 4) and temperature ...[more]

PMID: 32732961

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Project description:The influence of the side chains and positioning of the carboxy-terminal residues of NADPH-cytochrome P450 oxidoreductase (CYPOR) on catalytic activity, structure of the carboxy terminus, and interaction with cofactors has been investigated. A tandem deletion of residues Asp675 and Val676, that was expected to shift the position of the functionally important Trp677, resulted in higher cytochrome c reductase activity than that expected from previous studies on the importance of Asp675 and Trp677 in catalysis. Crystallographic determination of the structure of this variant revealed two conformations of the carboxy terminus. In one conformation (Mol A), the last α-helix is partially unwound, resulting in repositioning of all subsequent residues in β-strand 21, from Arg671 to Leu674 (corresponding to Ser673 and Val676 in the wild type structure). This results in the two C-terminal residues, Trp677 and Ser678, being maintained in their wild type positions, with the indole ring of Trp677 stacked against the isoalloxazine ring of FAD as seen in the wild type structure, and Ser673 occupying a similar position to the catalytic residue, Asp675. The other, more disordered conformation is a mixture of the Mol A conformation and one in which the last α-helix is not unwound and the nicotinamide ring is in one of two conformations, out towards the protein surface as observed in the wild type structure (1AMO), or stacked against the flavin ring, similar to that seen in the W677X structure that lacks Trp677 and Ser678 (1JA0). Further kinetic analysis on additional variants showed deletion or substitution of alanine or glycine for Trp677 in conjunction with deletion of Ser678 produced alterations in interactions of CYPOR with NADP+, 2'5'-ADP, and 2'-AMP, as well as the pH dependence of cytochrome c reductase activity. We postulate that deletion of bulky residues at the carboxy terminus permits increased mobility leading to decreased affinity for the 2'5'-ADP and 2'-AMP moieties of NADP+ and subsequent domain movement.

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Kinetic investigations of sulfite addition to flavanols.

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Kinetic investigations of sulfite addition to flavanols.

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