Quinohemoproteins

Ikeda T, Kobayashi D, Matsushita F, Sagara T, Niki K. 1993. Bioelectrocatalysis at electrodes coated with alcohol dehydrogenase, a quinohemoprotein with heme c serving as a built-in mediator. J Electroanal Chem 361 221-228. 

J. Razumiene, M. Niculescu, A. Ramanavicius, V. Laurinavicius, and E. Csoregi, Direct bioelectrocatalysis at carbon electrodes modified with quinohemoprotein alcohol dehydrogenase from Gluconobacter sp. 33. Electroanalysis 14, 43—49 (2002). 

M. Niculescu, T. Erichsen, V. Sukharev, Z. Kerenyi, E. Csoregi and W. Schuhmann, Quinohemoprotein alcohol dehydrogenase-based reagentless amperometric biosensor for ethanol monitoring during wine fermentation, Anal. Chim. Acta, 463(1) (2002) 39-51. 

It has been proposed that the substrate conversion is at the flavin site and the electrons are then transferred via Fe-S- and the heme to the electrode (ubiquinone in the native system). The electron transfer at the heme moiety has been confirmed with another quinohemoprotein using electroreflectance [114]. Since then a number of examples supporting this model have appeared (Fig. 2.7). 

D-Fructose dehydrogenase (EC 1.1.99.11) from Gluconobacter industrius is a 140 kDa membrane-bound quinohemoprotein with a PQQ and a heme c-containing subunit. 

Ethanol sensors were fabricated using the membrane-bound quinohemoprotein alcohol dehydrogenase (EC 1.1.99.8) from different sources and... 

Recently, Schuhmann et al. reported ethanol biosensors by entrapping quinohemoprotein alcohol dehydrogenase and Os-complex-modified poly(vinyl imidazole) during the electrochemically induced deposition of the poly(acrylate)-based resin [80]. The sensor exhibited its efficiency and also sufficient stability for practical applications. Author claims that the reported sensor preparation process is simple, easy to control, oxygen insensitive and can be applicable to other enzyme sensors. 

Figure 16.2-37. Resolution of alcohols by enantioselective oxidation using quinohemoprotein dehydrogenases (QHDH) from different microorganisms.

Figure 6 Structure and relative orientations of the CTQ and heme cofactors in quinohemoprotein amine dehydrogenase from P. denitrificans. In this enzyme, oxygenation of 7Trp43 and cross-linking with 7Cys37 yields the CTQ cofactor. CTQ and the two hemes present on the a subunit are displayed as sticks colored gray for carbon, red for oxygen, blue for nitrogen, yellow for sulfur, and dark red for iron. The coordinates from PDB entry 1 pby were used to display this structure.

Scheme 12 The reaction mechanism of CTQ-dependent quinohemoprotein amine dehydrogenase.

A direct electron transfer from entrapped quinohemoprotein alcohol dehydrogenase (QH-ADH) to a Pt electrode, via chains of the polypyrrole, acting as immobilization matrix, was demonstrated [152]. QH-ADH is able to translocate in a fast inner-enzymatic reaction, the electrons primarily accepted by PQQ to heme units located close to the outer protein shell, from where they can be transferred on the conducting-polymer chains (Fig. 13). A similarity between the electron-transfer pathway in multicofactor proteins and that of mediator-modified electroenzymes is apparent, if one considers that a multicofactor enzyme can be regarded as a combination of a primary redox site and protein-integrated electron-transfer relays. 

Evidence for the direct electron transfer from PPy to an entrapped quinohemoprotein alcohol dehydrogenase (QH-ADH) from Gluconobacter sp.33 prepared via an in situ polymerization of pyrrole in the presence of QH-ADH has been demonstrated by Ramanavicius et aL [70]. It was proposed that the cooperative action of the pyrroloquino-line-quinone (PQQ) and heme-containing enzymes permit electron transfer from the enzyme active site to the ICP. Ethanol is said to diffuse to the PQQ enzyme centre where it is oxidized to an aldehyde. The PQQ centre is subsequently regenerated by the heme sites in the enzyme. Resulting is an electron that can be readily transferred to the PPy at a viable kinetic rate. 

Ramanavicius, A., K. Habermuller, E. Csoregi, V. Laurinavicius, and W. Schuhmann. 1999. Poly-pyrrole-entraped quinohemoprotein alcohol dehydrogenase. Evidence for direct electron transfer via conducting-polymer chains. Anal Chem 71 3581. 

Enzymatic methods for alcohol determination frequently rely on the activity of alcohol oxidase alone or combined with horseradish peroxidase alcohol, quinohemoprotein alcohol dehydrogenase, or pyrroloquinoline quinine-dependent dehydrogenases. The enzymes are usually incorporated into biosensors for automated and routine application. The reaction may be followed by monitoring the concentration of either NADH or hydrogen peroxide produced in the reaction. The concentration of NADH is determined by its ultraviolet (UV) absorbance at 340 nm, and amperometric or... 

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