Formation of higher polyphenols

A laccase-like copper-containing phenol oxidase in Rhizoctonia praticola, optimum pH 6.7-6.9 and molecular weight 78 000, converts 2,6-dimethoxyphenol into 3,3',5,5'-tetramethoxybiphenoquinone [A3836].

Formation of higher polyphenols

Bjerkandera adusta manganese peroxidase (E.C. 1.11.1.13) converts guaiacol into a mixture of polymers, molecular weights up to about 3200. A range of other phenols, syringic acid and o-anisidine are also substrates [K565].

Trimerisation of indole

Oak, horse chestnut and Rhus oxidize indole to 2,2'-bis(3-indolyl)indoxyl [A3125].

Pterostilbene dimerisation

Botrytis cinerea laccase-like stilbene oxidase converts pterostilbene into a dimer (3-(3,5-dimethoxyphenyl)-5-(2-(3,5-dimethoxyphenyl) ethenyl)-2-(p -hydroxyphenyl)benzofuran) [K147].

Coniferyl alcohol dehydrogenase (E.C. 1.1.1.194)

Prunus strobus, Abies balsama, Laryx laricina, Picea rubens and Pinus banksiana enzymes act on coniferyl alcohol to form dehydrodiconiferyl alcohol and pinoresinol. The reactions involve condensation of the side chain to the aryl nucleus to form dehydrodiconiferyl alcohol, and between two side chains of coniferyl alcohol to form pinoresinol. Several isozymes are involved, which are glycoproteins [G745].

Sitka spruce (Picea sitchensis) xylem contains two glycoprotein isozymes, molecular weights 62000 or 80000 (depending on method; the higher value may be a methodological artifact); it is not a peroxidase [J820].

Berbabamunine synthase (E.C. 1.1.3.34)

Berberis stolonifera enzyme is a P450, molecular weight 46 000, pI 6.05 and optimum pH 8-8.5 or 7.2 /7.5, depending on conditions. Substrates include (R)- and (S)-N-methylcoclaurine, and (S)-coclaurine, which are dimerized by stereo-specific oxidative phenol coupling, without transfer of activated oxygen to the substrate molecules [G736].

Vindoline dimerisation

Streptomyces griseus catalyzes the formation of a complex dimer from vindoline, probably via dihydrovindoline ether that involves a head-to-head C-C bond formation adjacent to the non-indole nitrogen [A2984].

1.5 Reactions involving carbon ring fission

Catechol 1,2-dioxygenase (pyrocatechase; E.C. 1.13.11.1)

Catechol 0cis, cis-muconate

Rhodococcus rhodochrous enzyme, a homodimer with optimum pH 9, acts on catechol, 3- and 4-methylcatechol. The molecular weight of the monomer, based on mass spectrometry and genetic coding is 31 558 or 31 539, respectively [J703]. R. erythropolis enzyme, monomeric molecular weight 36000-37000 contains 1.3 mol Fe/mol. Pyrogallol, as well as catechol, 3-and 4-methylcatechol are substrates, but protocatechuate is not. It is inactivated at 50°. Its amino acid composition has been determined [D247].

Acinetobacter radioresistens enzyme is a homodimer, molecular weight 78 000. It is unusual in that it dissociates into an active monomer in 0.5M sodium sulphate. It contains 0.96 mol Fe3 +/subunit. It is more highly specific than Rhodococcus rhodochrous enzyme; 3- and 4-methylcatechol are poor substrates [J390].

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