Umbelliferone and Esculetin: Inhibitors or Substrates for Polyphenol Oxidases?

• Published in: Biological & Pharmaceutical Bulletin Vol. 31; no. 12; pp. 2187 - 2193
• Main Authors: Sollai, Francesca, Zucca, Paolo, Sanjust, Enrico, Steri, Daniela, Rescigno, Antonio
• Format: Journal Article
• Language: English
• Published: Japan The Pharmaceutical Society of Japan 2008; Pharmaceutical Society of Japan
• Subjects: Agaricus - enzymology; Catechol Oxidase - antagonists & inhibitors; Catechol Oxidase - metabolism; Electrophoresis, Polyacrylamide Gel; Enzyme Inhibitors - pharmacology; esculetin; Ferula - chemistry; Ferula communis; Glycosides - metabolism; Glycosides - pharmacology; laccase; Laccase - chemistry; Oxidation-Reduction; Pleurotus - chemistry; polyphenol oxidase; Pregnenolone - analogs & derivatives; Pregnenolone - metabolism; Pregnenolone - pharmacology; Software; Spectrophotometry, Ultraviolet; tyrosinase; umbelliferone; Umbelliferones - metabolism; Umbelliferones - pharmacology
• ISSN: 0918-6158; 1347-5215
• DOI: 10.1248/bpb.31.2187

Recently, an interesting debate arose about the nature (substrate versus inhibitor) of esculetin, a coumarin derivative, for mushroom polyphenol oxidase (PPO). The present study examined the behavior of PPOs preparations from fungal and plant origin towards esculetin as a substrate. Both enzymes were able to oxidize esculetin though at a slow rate. A higher sensitivity was reached when the assay was performed in the presence of 3-methyl-2-benzothiazolinone hydrazone (MBTH) even with a lower amount of PPO. These observations unambiguously confirmed that esculetin has to be considered a substrate for mushroom polyphenol oxidase. The oxidation of esculetin was also demonstrated for the first time by a fungal laccase. This should be taken into account because some mushroom PPO preparations could exert contaminant laccase activity. In addition, a PPO preparation from Ferula communis was demonstrated to use esculetin as a substrate. Umbelliferone, the monophenolic precursor of esculetin along the phenylpropanoid pathway, behaved as a competitive inhibitor for the monophenolase activity of mushroom PPO with a Ki value=0.014 mM. This is worth a mention because only a few couples of mono- and corresponding o-diphenol show such opposite behavior towards PPO. A possible role of PPO in the esculetin fate along biosynthesis pathway of coumarin derivatives is also discussed.