The metabolism of cycloalkanes by different species of Xanthobacter

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Warburton, E.J., 1989. The metabolism of cycloalkanes by different species of Xanthobacter. PhD, Nottingham Trent University.

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Abstract

The metabolism of cycloalkanes by different species of Xanthobacter E. Jean Warburton, 1989 Five members of the genus Xanthobacter were investigated with regard to their ability to metabolise cycloalkanes. Two of these microorganisms, Xanthobacter sp. and Xanthobacter autotrophicus 853 were capable of growth on the recalcitrant hydrocarbon cyclohexane. Xanthobacter autotrophicus 431 was capable of growth on cyclohexanol. Whole cell studies and enzymatic studies with cell- free extracts indicated the route of degradation of cyclohexane and cyclohexanol by X. autotrophicus 853 and X. autotrophicus 431 respectively to proceed via cyclohexane → cyclohexanol cyclohexanone→1-oxa-2-oxo-cycloheptane →adipic acid.

Xanthobacter sp. was investigated further to gain more knowledge of the enzymes involved in cyclohexane metabolism. Cyclohexane hydroxylase was found to possess a pH optimum of 6.8 and a broad substrate specificity including alkyl substituted cycloalkanes, aromatic hydrocarbons, bicyclic terpenes and heterocyclic rings although no activity was demonstrated towards n-alkanes. The enzyme was shown to be multicomponent and cytochrome P-450 containing. Cytochrome P-450 was found to be induced concomitantly with cyclohexane hydroxylase when Xanthobacter sp. was grown on cyclohexane. Cytochrome P-450 was stabilised by the addition of glycerol (10% v/v) and was found to have a molecular weight of 58,000. Attempts to purify cyclohexane hydroxylase were unsuccessful although partial purification of cytochrome P-450 has been obtained.

Cyclohexanol dehydrogenase from Xanthobacter sp. was purified 30.4 fold and found to have a pH optimum of 10.3. Cyclohexanone was identified as the reaction product. The enzyme possessed a broad specificity for secondary alcohols, a molecular weight of 44,000 and a requirement for NAD+ and to a lesser extent NADP+. The apparent Km for NAD+ was determined as l4.3μM.

Whole cell and enzymatic studies with Xanthobacter sp. indicated that methylcyclohexane is metabolised by the same route as cyclohexane, by hydroxylation on the ring and not by attack of the methyl substituent.

Item Type:

Thesis

Creators:

Warburton, E.J.

Date:

1989

ISBN:

9781369324235

Identifiers: