Pyrroloquinoline quinone glucose

Yoshida, H., Kojima, K., Witarto, A. B., and Sode, K. (1999). Engineering a chimeric pyrroloquinoline quinone glucose dehydrogenase improvement of EDTA tolerance, thermal stability and substrate specificity. Protein Eng., 12, 63-70. 

Yoshida H, Iguchi T, Sode K (2000) Construction of multi-chimeric pyrroloquinoline quinone glucose dehydrogenase with improved enzymatic properties and application in glucose monitoring. Biotechnol Lett 22(18) 1505-1510... 

Hamamatsu N, Suzumura A, Nomiya Y, Sato M, Aita T, Nakajima M, Husimi Y, Shibanaka Y (2006) Modified substrate specificity of pyrroloquinoline quinone glucose dehydrogenase... 

Zayats M, Katz E, Baron R, Willner I. 2005. Reconstitution of apo-glucose dehydrogenase on pyrroloquinoline quinone-functionalized Au nanoparticles yields an electrically contacted hiocatalyst. J Am Chem Soc 127 12400-12406. 

Examples of surface-immobilized mediators are electropolymerized azines for electro-oxidation of The extreme form of this approach is formation of biocatalytic monolayer, comprising a surface-bound mediator species that is itself bound to a single enzyme molecule. Katz et al. report a complete cell based on novel architecture at both electrodes (Figure 7). On the anode side, the FAD center of glucose oxidase is removed from the enzyme shell and covalently attached to a pyrroloquinoline quinone (PQQ) mediator species previously immobilized on a gold surface. The GOx apoenzyme (enzyme with active center removed) is reintroduced in solution and selectively binds to FAD, resulting in a PQQ-... 

M. Niculescu, R. Mieliauskiene, V. Laurinavicius and E. Csoregi, Simultaneous detection of ethanol, glucose and glycerol in wines using pyrroloquinoline quinone-dependent dehydrogenases based biosensors, Food Chem., 82(3) (2003) 481 89. 

All potentials vs. screen-printed Ag/AgCl pseudo-reference, except values marked with asterisk ( ), which are vs. Ag/3M AgCl double-junction reference electrode, and values marked with dagger CfO, which are vs. saturated calomel. Abbreviations CoPC cobalt phthalocyanine, SPCE screen-printed carbon electrode, GOD glucose oxidase, MWCNT multi-walled carbon nanotubes, NAD nicotinamide adenine dinucleotide, PQQ pyrroloquinoline quinone, FIA flow injection analysis. 

An alternative biosensor system has been developed by Hart et al. [44] which involves the use of the NAD+-dependent GDH enzyme. The first step of the reaction scheme involves the enzymatic reduction of NAD+ to NADH, which is bought about by the action of GDH on glucose. The analytical signal arises from the electrocatalytic oxidation of NADH back to NAD+ in the presence of the electrocatalyst Meldola s Blue (MB), at a potential of only 0Y. Biosensors utilising this mediator have been reviewed elsewhere [1,17]. Razumiene et al. [45] employed a similar system using both GDH and alcohol dehydrogenase with the cofactor pyrroloquinoline quinone (PQQ), the oxidation of which was mediated by a ferrocene derivative. 

Willner et al. [52] have created some elegant interfacial supramolecular assemblies to address this issue by removing the non-covalently bound flavin adenine dinucleotide (FAD) redox center from glucose oxidase and immobilizing the enzyme on a tether consisting of cystamine chemisorbed on a gold surface, a pyrroloquinoline quinone (PQQ) link and FAD. The mediator potential and electron transfer distances of this assembly were carefully chosen so that transfer of electrons from the FAD to the PQQ and to the electrode is very fast. A maximum rate of 900 150 s-1 for the enzymatic reaction within this monolayer assembly was obtained, which is indistinguishable from the value of about 1000 s-1 obtained for the enzyme in solution. While monolayers can offer molecular-level control of the interfacial structure, the... 

Modified electrodes for this analytical purpose have mostly been formed by electrode adsorption of the mediator systems on the electrode surface or by electropolymerization [24,116]. Recently, for example, NAD(P)H oxidations have been performed on platinum or gold electrodes modified with a monolayer of pyrroloquinoline quinone (PQQ) [117] or on poly(methylene blue)-modified electrodes with different dehydrogenases entrapped in a Nafion film for the amperometric detection of glucose, lactate, malate, or ethanol [118]. In another approach, carbon paste electrodes doped with methylene green or meldola blue together with diaphorase were used for the NADH oxidation [119]. A poly(3-methylthio-phene) conducting polymer electrode was efficient for the oxidation of NADH [120]. By electropolymerization of poly(aniline) in the presence of poly(vinylsulfonate) counterions. 

An analogous amplification process for determination of phenols was proposed based on the kinetics of disappearance of /1-NADH reacting with quinone, which is derived from a phenol in a tyrosinase-catalyzed oxidation. LOD was as low as 50 nM in a 10 min assay . Amplification cycles were also achieved by combining a Pt electrode where phenols are oxidized with a polyurethane layer embedding pyrroloquinoline quinone-dependent glucose dehydrogenase, to catalyze the reduction of the oxidation products . 

Thym, D., Knappe, W.-R. (2003) Variants of soluble pyrroloquinoline quinone-dependent glucose. EP 1332216. 

Alternatively, electrochemical detection by using an amperometric biosensor has been proposed using modified electrodes for the electrocatalytic oxidation of the reduced cofactors (NADH, NADPH). The oxidation current reflects the rate of glucose conversion. Additionally, covalent coupling of the coenzyme is a precondition of more advanced reagentless measuring devices. Further developments use an electron mediator such as ferrocyanide and PQQ/ PQQHi (pyrroloquinoline quinone) as the cofactor pair. 

---