Color reaction of amino acids and proteins with ethyl caffeate.

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  • カフェ酸エチルエステルによるアミノ酸およびタンパク質の呈色反応について
  • カフェサン エチルエステル ニ ヨル

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It is known that an alkaline solution of ethyl caffeate yields a green color product in the presence of nitrogen-containing compounds such as amino acids or proteins. In this investigation basic and applied studies on this greening phenomenon were conducted. On heating, ethyl caffeate reacted with amino acids having an aromatic ring or an imidazole ring as a side-chain to rapidly yield a greencolored product with a maximal light absorbance at 695-700nm in the visible range. Amino acids with an aliphatic primary amine resulted in equally rapid greening, but λmax was observed at 675-676nm. Amino acids with a branched chain at the β carbon appeared to have poor reactivity with ethyl caffeate, whereas cysteine with a reducible thiol group, and proline, in which the α amino group is substituted, did not react completely. In the case of proteins, it appeared that the amino groups of lysine residues reacted with ethyl caffeate to form a green-colored product on protein molecules. Further investigation demonstrated that this reaction could be utilized for the quantitative estimation of very small amounts of proteins. The addition of keto acid to a mixture of ethyl caffeate and nitrogen-containing compounds resulted in an increase in the corresponding green product.

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