Yasunori Ohashi

De novo synthesis of (Z)- and (E)-7-hexadecenylitaconic acids by a selective lignin-degrading fungus, Ceriporiopsis subvermispora.

Ceriporic acids are a class of alk(en)ylitaconic acids produced by a selective lignin-degrading fungus, Ceriporiopsis subvermispora. Their structural units have similarity with biologically important lichen acids, such as chaetomellic and protolichesterinic acids. The unique function of alkylitaconic acid is the redox silencing of the Fenton reaction system by inhibiting reduction of Fe(3+). As estimated by the catalytic function of Delta9-desaturases, 7-hexadecenyl derivatives bearing a trans configuration have not been reported in the family of alk(en)ylitaconic acids, i.e. the structurally similar lichen acids-alk(en)ylcitraconic and paraconic acids. In this paper, we discuss the isolation of an itaconic acid derivative with an (E)-7-hexadecenyl chain from cultures of C. subvermispora. To identify the natural metabolite, (E)- and (Z)-7-hexadecenylitaconic acids were chemically synthesised. The isolated metabolite was identical to the synthetic (E)-hexadecenylitaconic acid and was designated as ceriporic acid D. Administration of (13)C-[U]-glucose demonstrated that ceriporic acid C and trans-7-hexadecenylitaconic acid (ceriporic acid D) were biosynthesised de novo by C. subvermispora.

A novel method of measuring hydroxyl radical-scavenging activity of antioxidants using γ-irradiation

A new method using ESR spin trapping was proposed for measuring the scavenging activity of antioxidants for the hydroxyl (OH) radical. (-)-Epigallocatechin gallate (EGCg) and 5,5-dimethyl-1-pyrrolline N-oxide (DMPO) were used as the antioxidant and spin trapping agent, respectively. The conventional method using a Fenton reaction had problems associated with the estimation of activity, because the antioxidant disturbs the system for generating OH radical by coordinating on Fe2+ and by consuming H2O2, besides scavenging the spin adduct (DMPO-OH). Intense γ-irradiation was therefore used to generate OH radicals, and the intensity decrease in DMPO-OH after irradiation was followed to obtain the rate constant for the scavenging of DMPO-OH by EGCg. The intensities were extrapolated to zero time to estimate the quantity of DMPO-OH formed during γ-irradiation. By using these values, the reaction rate constant between OH radical and EGCg was calculated as a ratio to that of DMPO. It was shown that this method is useful for comparing the OH radical-scavenging activity of various antioxidants.

Degradation of sulfide linkages between isoprenes by lipid peroxidation catalyzed by manganese peroxidase.

Scission of sulfide linkages in vulcanized rubber has been a major concern since the early 20th century, because devulcanization is a key process for recycling waste rubber products as polymer materials that pose low environmental risks. We herein demonstrate that lipid peroxidation (LPO) of linoleic acid by manganese peroxidase (MnP), a proposed lignin-degradation system in the early stage of selective white rot fungi, cleaves sulfide bond in a model rubber compound, di(2-methylpent-2-enyl) sulfide, to 2,4-dimethylthiophene and 2-methyl-2-pentenal. The major intermediate of the LPO process, 2,4-decadienal was directly oxidized by MnP to cleave the sulfur-carbon bond. We propose that electrophilic radicals from 2,4-decadienal abstract one electron from a sulfur atom of the model compound to produce the sulfur radical cation intermediate, which in turn reacts with molecular oxygen to cleave the sulfur-carbon bond. The discovery of free radical-mediated scission of sulfide bond coupled with Mn oxidation provides a novel strategy for recycling vulcanized rubber wastes.

Protective effect of tea catechins on the DNA scission induced in tritiated water

ABSTRACT The protecting effect of (−)-epicatechin (EC), (−)-epicatechin gallate (ECg), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg) and 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) on the DNA strand scission induced in tritiated water was analyzed. The scission with the hydroxyl radical produced by the decomposition of water molecules was decreased by the addition of above reagents. Protective effect of EGCg, EC and DMPO was dependent on their concentrations, but that of ECg and EGC was independent. Therefore, it was considered that certain amounts of ECg, EGC molecules might locate around DNA molecules, interacting with DNA.

Scavenging activity of tea catechins on hydroxyl radical formed in tritiated water studied by the solid-state spin trapping method

ABSTRACT Solid state spin trapping method was applied for measuring the scavenging activity of hydroxyl (OH) radical formed by the beta ray from tritiated water with four tea catechins, (−)-epicatechin (EC), (−)-epicatechin gallate (ECg), (−)-epigallocatechin (EGC) and (−)-epigallocatechin gallate (EGCg). The activity was in the order of EGCg > ECg > EGC > EC. This is consistent with the order of the number of phenolic hydroxyl groups in each catechin molecule. However, it was shown that EGCg had stronger activity than others, which suggested the interaction between the B ring and the gallate group.