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

抄録

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.