Degradation Mechanism of Poly(vinyl alcohol) by Successive Reactions of Secondary Alcohol Oxidase and β-Diketone Hydrolase from Pseudomonas sp.

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The secondary alcohol oxidase from Pseudomonas sp. catalyzed the oxidation of various vinyl alcohol oligomers with the molecular weight of 220 to 1500 and of β-ketols such as 5-hydroxy-3-heptanone, 4-hydroxy-2-nonanone, 3-hydroxy-5-nonanone, 6-hydroxy-4-nonanone, 7-hydroxy-5-dodecanone, and 8-hydroxy-6-tridecanone. β-Diketone hydrolase from the same strain catalyzed the hydrolysis of various aliphatic β-diketones and some aromatic β-diketones such as l-phenyl-1, 3-butanedione and 1-phenyl-2, 4-pentanedione. 4, 6-Nonanediol, used as a low molecular weight model of poly(vinyl alcohol) (PVA), was oxidized to 4, 6-nonanedione by way of 6-hydroxy-4-nonanone by secondary alcohol oxidase. 4, 6-Nonanedione was hydrolyzed to 2-pentanone and nbutyric acid by β-diketone hydrolase. These reactions were stoichiometric. The presence of the β-diketone structure in PVA oxidized by secondary alcohol oxidase was confirmed by spectral experiments. The absorption due to β-diketone structure in the oxidized PVA decreased as it was hydrolyzed by β-diketone hydrolase. The ratio of the amount of carboxyl groups in the degraded PVA to that of carbonyl groups in the oxidized PVA became more than 0.5. A pathway for the enzymatic degradation of PVA was proposed.
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