Investigation of the Mechanism of Action of Pyrogallol-Phloroglucinol Transhydroxylase by Using Putative Intermediates

• Published in: Chemistry : a European journal Vol. 13; no. 10; pp. 2805 - 2811
• Main Authors: Paizs, Csaba, Bartlewski-Hof, Ulrike, Rétey, János
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-01-2007; WILEY‐VCH Verlag
• Subjects: Anaerobiosis; Binding Sites; Catalysis; Coenzymes - metabolism; Crystallography, X-Ray; enzymes; ethers; Hydroxylation; Metalloproteins - metabolism; Models, Chemical; molybdopterin (Moco); OH transfer; Oxidoreductases - metabolism; Phenols - chemical synthesis; Phenyl Ethers - chemical synthesis; Proteobacteria - enzymology; Pteridines - metabolism; reaction mechanisms; Water - chemistry
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200601053

Pyrogallol–phloroglucinol transhydroxylase from Pelobacter acidigallici, a molybdopterin‐containing enzyme, catalyzes a key reaction in the anaerobic degradation of aromatic compounds. In vitro, the enzymatic reaction requires 1,2,3,5‐tetrahydroxybenzene as a cocatalyst and the transhydroxylation occurs without exchange with hydroxy groups from water. To test our previous proposal that the transfer of the hydroxy group occurs via 2,4,6,3′,4′,5′‐hexahydroxydiphenyl ether as an intermediate, we synthesized this compound and investigated its properties. We also describe the synthesis and characterization of 3,4,5,3′,4′,5′‐hexahydroxydiphenyl ether. Both compounds could substitute for the cocatalyst in vitro. This indicates that the diphenyl ethers can intrude into the active site and initiate the catalytic cycle. Recently, the X‐ray crystal structure of the transhydroxylase (TH) was published16 and it supports the proposed mechanism of hydroxy‐group transfer.
Reaction mechanisms: What does molybdopterin (Moco) do in transhydroxylation? In contrast to previous beliefs, the hydroxy transfer occurs directly from the tetrahydroxybenzene cocatalyst to the quinone form of pyrogallol (see scheme). Moco is solely a redox agent and the newly synthesized 2,4,6,3′,4′,5′‐hexahydroxydiphenyl ether is an intermediate.