Summary: The membrane-bound aldehyde dehydrogenase from ‘’ CCM 1774, solubilized from the membrane fraction by treatment with surfactants and subsequently purified to homogeneity, was characterized with respect to the of the dimeric enzyme (145000), pH optimum (5·1), pI value (5·3), substrate specificity towards straight-chain aldehydes, substrate inhibition and the effects of various inhibitors and ions. Methanol extracts of the membrane fraction and of the purified enzyme showed properties identical with pyrroloquinoline quinone as revealed by spectrophotometric methods and reactivity with apoquinoprotein glucose dehydrogenase. Pyrroloquinoline quinone could not be liberated by EDTA treatment. The enzyme activity of an apoenzyme could be partly restored by addition of membrane extracts containing pyrroloquinoline quinone adducts. The solubilized, purified quinoprotein aldehyde dehydrogenase and the membrane-bound enzyme differed in substrate binding, substrate inhibition, pH optimum and linkage to a -type cytochrome which acts as electron acceptor in membrane fractions. Since double-reciprocal plots of initial reaction rates with various concentrations of aldehyde or electron acceptor showed intersecting lines, and different inhibition patterns were obtained for the two forms of the enzyme, a ping-pong kinetic behaviour with the two reactants was excluded. The kinetic mechanism was suggested to be changed after solubilization from a random-order type to a compulsory-order type, and is thus atypical for quinoproteins reported so far.


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