Studies on Biochemical Functions of Pyrroloquinoline Quinone

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The quinoprotein dehydrogenase has been classified into four groups according to their localization and characterization :(1) methanol dehydrogenase in methylotrophs,(2) quinoprotein alchold dehydrogenase from non-methylotrophic bacteria, when they are grown on ethanol as sole carbon source.(3) Quinohemoprotein alcohol dehydrogenase is formed as apo-enzyme in Commamonas testosteroni, while Pseudomonas putida forms holo-enzyme when they are grown on primary alcohols as the carbon source.(4) Quinohemoprotein alcohol dehydrogenase-cytochrome c complex is formed is formed in the cytoplasmic membranes of acetic acid bacteria.During the course of this research program, the following new findings have been added to clear up the function of pyrroloquinoline quinone and quinoproteins.(1) Membrane-bound, pyrroloquinoline quinone-dependent, alcohol dehydrogenase functions as the primary dehydrogenase in the respiratory chain of acetic acid bacteria. An ability of the enzyme to directly react with … More ubiquinone was investigated in alcohol dehydrogenases purified from both Acetobacter aceti and Gluconobacter suboxydans. The reconstitution of alcohol oxidase was done by binding the detergent-free dehydrogenase at room temperature to proteoliposomes that had been prepared in advance from a ubiquinol oxidase and phospholipids containing ubiquinone by detergent dialysis using octyl-glucoside. The proteoliposomes thus reconstituted had a reasonable level of ethanol oxidase activity, the electron transfer reaction of which was also able to generate a membrane potential.(2) Methanol and ethanol oxidase respiratory chains of the methylotrophic acetic acid bacterium, Acetobacter methanolicus, was investigated. In this study, an 32 KDa peptide was found in alternative type of methanol dehydrogenase which contained three different subunits two of which corresponded to alpha-subunit and beta-subunit. The third subunit was finally concluded to be the MoxJ product in methanol oxidase, because the N-terminal amino acid sequence of the peptide showed a high homology to that of MoxJ gene from Paracoccus denitrificans or Methylobacterium extorquens AMl.(3) Pseudomonas putida HK5, isolated from soil and identified thereafter, produced three different quinoprotein alcohol dehydrogenase as holo-enzyme. When grown on ethanol, it produced a quinohemoprotein alcohol dehydrogenase, While grown on glycerol, another quinohemoprotein alcohol dehydrogenase which can oxidize glycerol. The third type of quinoprotein alcohol dehyderogenase was similar to those found in non-methylotrophic bacteria which were grown on ethanol. The third alcohol dehydrogenase contained no heme component and was not able to oxidize alcohol with potassium ferricyanide as an electron acceptor. Less