Kinetic Analysis of Terminal and Unactivated C?H Bond Oxyfunctionalization in Fatty Acid Methyl Esters by Monooxygenase-Based Whole-Cell Biocatalysis

The alkane monooxygenase AlkBGT from Pseudomonas putida GPo1 constitutes a versatile enzyme system for the omega-oxyfunctionalization of medium chain-length alkanes. In this study, recombinant Escherichia coli W3110 expressing alkBGT was investigated as whole-cell catalyst for the regioselective biooxidation of fatty acid methyl esters to terminal alcohols. The omega-functionalized products are of general economic interest, serving as building blocks for polymer synthesis. The whole-cell catalysts proved to functionalize fatty acid methyl esters with a medium length alkyl chain specifically at the omega-position. The highest specific hydroxylation activity of 104 U g(CDW)-(1) was obtained with nonanoic acid methyl ester as substrate using resting cells of E. coli W3110 (pBT10). In an optimized set-up, maximal 9-hydroxynonanoic acid methyl ester yields of 95% were achieved. For this specific substrate, apparent whole-cell kinetic parameters were determined with a V-max of 204 +/- 9 U g(CDW)(-1), a substrate uptake constant (K-S) of 142 +/- 17 mu M, and a specificity constant V-max/K-S of 1.4 U g(CDW)(-1) mu M-1 for the formation of the terminal alcohol. The same E. coli strain carrying additional alk genes showed a different substrate selectivity. A comparison of biocatalysis with whole cells and enriched enzyme preparations showed that both substrate availability and enzyme specificity control the efficiency of the whole-cell bioconversion of the longer and more hydrophobic substrate dodecanoic acid methyl ester. The efficient coupling of redox cofactor oxidation and product formation, as determined in vitro, combined with the high in vivo activities make E. coli W3110 (pBT10) a promising biocatalyst for the preparative synthesis of terminally functionalized fatty acid methyl esters.