When quinones meet amino acids: chemical, physical and biological consequences

Abstract

Quinones and amino acids are usually compartmentally separated in living systems, however there are several junctions in which they meet, react and influence. It occurs mainly in wounded, cut or crushed plant material during harvest, ensiling or disintegrating cells. Diffusing polyphenols are oxidized by polyphenol oxidases (PPOs) to quinonic compounds, which associate reversibly or irreversibly with amino acids and proteins. The reaction takes place with the free nucleophilic functional groups such as sulfhydryl, amine, amide, indole and imidazole substituents. It results in imine formation, in 1,4-Michael addition via nitrogen or sulphur and in Strecker degradation forming aldehydes. The formation and activity of quinone-amino acids conjugates influences the colour, taste, and aroma of foods. Physical and physiological phenomena such as browning of foods, discoloration of plants during processing, alteration of solubility and digestibility, formation of humic substances, germicidal activity, cytotoxicity and more occur when quinones from disintegrating cells meet amino acids. The mechanisms of toxicity and the pathways by which PCBs may be activated and act as a cancer initiator include oxidation to the corresponding quinones and reaction with amino acids or peptides. Sclerotization of insect cuticle is a biochemical process involving also the reaction between quinones and amino acid derivatives.

Complementary Genes That Cause Black Ripening Hulls in F1Plants of Crosses betweenIndicaandJaponicaRice Cultivars

“…In higher plants, the brown or black pigmentation of tissues is caused mainly by polyphenol oxidase (Piližota and Šubarić, 1998;Bittner, 2006). Phenols are oxidized by polyphenol oxidases, and the resulting quinonic compounds associate with amino acids or proteins, producing brown pigmentation (Piližota and Šubarić, 1998;Bittner, 2006).…”

“…Phenols are oxidized by polyphenol oxidases, and the resulting quinonic compounds associate with amino acids or proteins, producing brown pigmentation (Piližota and Šubarić, 1998;Bittner, 2006). Furthermore, Bh4 was predicted to encode a tyrosine transporter, and the concentrations of tyrosine in hulls increased in the transformed rice plants with functional Bh4 gene (Zhu et al, 2011).…”

“…The frequency of the dominant allele of Phr1 was reported to be high in the indica and low in the japonica cultivars (Morishima and Oka, 1981;Yu et al, 2008). Polyphenol oxidase is known to oxidize phenols in plant tissues and to produce brown or black compounds (Piližota and Šubarić, 1998;Bittner, 2006); accordingly, the black hull pigmentation was suggested to be produced by the activity of polyphenol oxidase (Kuriyama and Kudo, 1967). Other complementary genes may be involved in the production of the phenol substrates (Kuriyama and Kudo, 1967); however, these genes have not yet been identified.…”

Plant polyphenols in cell-cell interaction and communication

“…18 of enzymatic and thermal browning process accompanying various traditional preparation of beverages (tea, coffee, cacao, beer and so on) and meal (roasted or baked vegetables and meet). 11 According to our hypotheses (Fig. 3) the polyphenols rich with gallate moieties may attach to the cell surface, change physical properties of lipids, initiate lateral segregation and formation of lipid and protein clusters, and finally, initiate binding of neighbouring cells.…”

“…However, after oxidation of catechol and gallate 10 moieties to quinones ( Fig. 1) in presence of peroxidases, polyphenol oxidases, alkaline pH, or transition metals they could be involved in reactions with free nucleophilic functional groups such as sulfhydryl, amine, amide, indole and imidazole substituents; 11 and result in covalent binding with different residues including lysine, methionine, cysteine and tryptophane. 8,12 We expect that terminal amino groups of phosphatidylethanolamines or sulfolipids of biological membranes can also participate in covalent binding with quinones.…”