Rubber-degrading activity was found in the extracellular culture medium of Xanthomonas sp. strain 35Y which was grown on natural rubber latex. Natural rubber in the latex state was degraded by the crude enzyme, and two fractions were separately observed by gel permeation chromatography of the reaction products. One fraction was of higher molecular weight (HMW) with a very wide MW distribution from 103 to 105, and the other fraction was of lower molecular weight (LMW) with a MW of a few hundred. 1H-nuclear magnetic resonance spectra of the partially purified fractions were those expected of cis-1,4-polyisoprene mixtures with the structure OHC-CH2-(-CH2-C(-CH3) = CH-CH2-)n-CH2-C(=O)-CH3, with average values of n of about 113 and 2 for HMW and LMW fractions, respectively. The LMW fraction consisted mostly of one component in gas-liquid chromatography as well as in gel permeation chromatography, and the main component was identified as 12-oxo-4,8-dimethyl trideca-4,8-diene-1-al (acetonyl diprenyl acetoaldehyde, AlP2At) by 13C-nuclear magnetic resonance and gas chromatography-mass spectra. Not only the latices of natural and synthetic isoprene rubber, but also some kinds of low-MW polyisoprene compounds of cis-1,4 type, were degraded by the crude enzyme. The rubber-degrading reaction was found to be at least partly oxygenase catalyzed from the incorporation of 18O into AlP2At under an 18O2 atmosphere.
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