Oxidation Of Caffeic Acid Research Articles

Ring cleavage of plant catechols by crystalline oxygenases

Abstract The aromatic ring of dihydroxyphenylpropanoids was found to be cleaved by two types of highly characterized crystalline oxygenases derived from bacteria. Oxidation of caffeic acid, chlorogenic acid, dihydroxyphenylalanine, and dihydroxyphenylethylamine by the intradiol and extradiol-cleaving enzymes, protocatechuate 3,4-dioxygenase and metapyrocatechase, respectively, permits description of rates and characteristics of the cleavage reactions and spectral properties of the products. The described reactions and oxidation products are pertinent to the study of plant aromatic metabolism and the degradation of plant constituents by soil bacteria.

O-Quinones formed in plant extracts. Their reactions with amino acids and peptides.

1. The reactions of amino acids and peptides with the o-quinones produced by the enzymic oxidation of chlorogenic acid and caffeic acid have been studied manometrically and spectrophotometrically. 2. Amino acids, except lysine and cysteine, react primarily through their alpha-amino groups to give red or brown products. These reactions, which compete with the polymerization of the quinones, are followed by secondary reactions that may absorb oxygen and give products with other colours. 3. The in-amino group of lysine reacts with the o-quinones in a similar way. The thiol group of cysteine reacts with the quinones, without absorbing oxygen, giving colourless products. 4. Peptides containing cysteine react with the o-quinones through their thiol group. 5. Other peptides, such as glycyl-leucine and leucylglycine, react primarily through their alpha-amino group and the overall reaction resembles that of the N-terminal amino acid except that it is quicker. 6. With some peptides, the secondary reactions differ from those that occur between the o-quinones and the N-terminal amino acids. The colours produced from carnosine resemble those produced from histidine rather than those from beta-alanine, and the reactions of prolylalanine with o-quinones are more complex than those of proline.

The mechanism of oxidation gelation of a glycoprotein from wheat flour: Evidence from a model system based upon caffeic acid

1. 1. A wheat-flour glycoprotein fraction, containing small amounts of esterified ferulic acid has the capacity to gel upon the addition of H 2O 2. This capacity is lost when traces of firmly bound Fe 3+ and Ca 2+ are removed (electrodialysis). The gelation capacity could be restored by subsequent addition of both ions, or by the addition of peroxidase (instead of Fe 3+ and other Group IIA metals (instead of Ca 2+). The gels, once formed, could be liquefied by deionisation and partly reconstituted by replacing the metal ions. 2. 2. Aqueous solutions of synthetic caffeoyl esters of guaram formed gels closely similar to those given by the glycoprotein when oxidised in the presence of Ca 2+. Unsubstituted guaran did not gel under these conditions. 3. 3. Kinetic studies of the oxidation of caffeic acid by H 2O 2 indicated that this consisted largely in the introduction of one or two additional hydroxyl groups into the aromatic nucleus, followed by further oxidation to give hydroxyquinones. This was supported by the identification of esculetin as an intermediate in the oxidation of cis-caffeic acid and the isolation of the hydroxy-quinones as stable calcium complexes, having a metal-ligand ration of 1:2. 4. 4. It is concluded that the oxidative gelation of caffeoyl guaran consists in the conversion of the caffeic acid ester groups into hydroxyquinonoid structures, followed by formation of intermolecular cross-linkages of the chelate-bridge type, and it is inferred that the gelation of the wheat-flour glycoprotein takes place by a similar mechanism.

Sulla azione di alcuni chinoni naturali sulla attività glucosio — 6 — P Deidrogenasica

Abstract INHIBITION OF GLUCOSE-6-P DEYDROGENASE BY OXIDATION PRODUCTS OF NATURAL PHENOLS. — The inhibition of Gl-6-P dehydrogenase activity found in highly concentrated homogenates from potato tuber tissue, seems due to natural occurring orto-di-quinones, such those arising from polyphenoloxidase catalized oxidation of chlorogenic acid, caffeic acid, and tyrosine. These compounds strongly inhibit Gl-6-P dehydrogenase activity of the potato tuber homogenate as well as that of purified Gl-6-P dehydrogenase from yeast. The inhibition effect appears much stronger when the diphenols are oxidized in the presence of the Gl-6-P dehydrogenase. Gl-6-P and TPN efficently protect the enzyme from the inhibition. Ascorbic acid prevents the inhibition by mantaining the diphenols in the reduced form, but is ineffective in reversing the inhibition.

The polyphenolase of tobacco and its participation in amino acid metabolism. I. Manometric studies

1. 1. An active polyphenolase has been isolated from tobacco free of any impurities which might interfere with manometric studies. 2. 2. Enzymic oxidation of catechol, caffeic acid, and chlorogenic acid has been studied. 3. 3. The phenolase of tobacco is capable of functioning similarly to that of other plants in relation to protein metabolism. 4. 4. Further evidence for the presently accepted mechanism of amino acid-oxidized polyphenol combination is presented.