Oxidative Pathway from Squalene to Geranylacetone in Arthrobacter sp. Strain Y-11

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The reaction pathway from squalene to trans-geranylacetone in Arthrobacter sp. strain Y-11 was studied. The enzyme or enzymes catalyzing squalene degradation were found to be membrane bound. Stoichiometric analysis of a cell-free system revealed that the ratio of squalene to trans-geranylacetone changed from 1:2 to 1:1 as the reaction proceeded, indicating two steps in geranylacetone formation. The initial step was found to be oxygenase catalyzed, from the absolute requirement for molecular oxygen in geranylacetone formation and the incorporation of 18O into geranylacetone under 18O2 atmosphere. By using [3H]squalene as the substrate, we detected an intermediate in the pathway and identified it as 5,9,13-trimethyltetradeca-4,8,12-trienoic acid by mass spectrometry, infrared spectrometry, nuclear magnetic resonance spectrometry, and chemical synthesis. We deduced that squalene was first oxidatively cleaved to geranylacetone and the intermediate, and that the intermediate was further metabolized to geranylacetone. We also synthesized some of the presumptive metabolites, such as 4,8,12-trimethyltrideca-4,8,12-trien-2-one, and confirmed that they served as active precursors for geranylacetone formation. Based on these lines of evidence, we present here the pathway from squalene to trans-geranylacetone in Arthrobacter sp. strain Y-11.

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