Pyrroloquinoline Quinone (PQQ) and Quinoprotein Enzymes

Abstract

This review summarises the characteristics, identification, and measurement of pyrroloquinoline quinone, the prosthetic group of bacterial quinoprotein dehydrogenases whose structures, mechanisms, and electron transport functions are described in detail. Type I alcohol dehydrogenase includes the "classic" methanol dehydrogenase; its x-ray structure and mechanism are discussed in detail. It is likely that its mechanism involves a direct hydride transfer rather than a mechanism involving a covalent adduct. The x-ray structure of a closely related ethanol dehydrogenase is also described. The type II alcohol dehydrogenase is a soluble quinohaemoprotein, having a C-terminal extension containing haem C, which provides an excellent opportunity for the study of intraprotein electron transfer processes. The type III alcohol dehydrogenase is similar but it has two additional subunits (one of which is a multihaem cytochrome c) bound in an unusual way to the periplasmic membrane. One type of glucose dehydrogenase is a soluble quinoprotein whose role in energy transduction is uncertain. Its x-ray structure (in the presence and absence of substrate) is described together with the detailed mechanism, which also involves a direct hydride transfer. The more widely distributed glucose dehydrogenases are integral membrane proteins, bound to the membrane by transmembrane helices at the N-terminus.

A Cluster of Four Homologous Small RNAs Modulates C 1 Metabolism and the Pyruvate Dehydrogenase Complex in Rhodobacter sphaeroides under Various Stress Conditions

“…In addition to FlhR-dependent effects of CcsR1-4, an FlhR-independent influence of CcsR1-4 on pqqA expression was observed. The PqqA peptide is a precursor of PQQ, which is an important redox cofactor in Gram-negative bacteria and is functionally related to C 1 metabolism (59)(60)(61).…”

Isolation and characterization of Pseudomonas sp. strain capable of degrading diethylstilbestrol

“…strain J51 were determined to be involved in the DES degradation. Quinoprotein alcohol dehydrogenase, which usually occupies PQQ as a cofactor and belongs to the family of PQQ-dependent type I alcohol dehydrogenase, participates in five well-known metabolic pathways (Anthony 2001). In this study, the gene-encoding quinoprotein alcohol dehydrogenase of Pseudomonas sp.…”

Isolation and characterization of mineral phosphate-solubilizing bacteria naturally colonizing a limonitic crust in the south-eastern Venezuelan region

“…These acids are produced in the periplasm of many Gram-negative bacteria through a direct oxidation pathway of glucose (DOPG, non-phosphorylating oxidation) whose physiological role remains uncertain (Anthony, 2001(Anthony, , 2004 Matsushita et al, 2002). The enzymes of the DOPG, the quinoproteins glucose dehydrogenase (GDH) and gluconate dehydrogenase (GADH), are oriented to the outer face of the cytoplasmic membrane so that they oxidize their substrates in the periplasmic space (Anthony, 2004).…”