Escherichia coli, aldehyde oxidation

Transketolase (EC 2.2.1.1) is involved in the oxidative pentose phosphate pathtvay in tvhich it catalyzes the reversible transfer of a hydroxyacetyl nucleophile bettveen a variety of sugar phosphates. The enzyme, tvhich requires thiamine diphosphate and divalent Mg as cofactors [248], is commercially available from baker s yeast and can be readily isolated from many natural or recombinant sources [249, 250]. The yeast enzyme has been structurally tvell characterized [251], including protein tvith a carbanion intermediate covalently bound to the cofactor [252]. Large-scale enzyme production has been investigated for the transketolase from Escherichia coli [253-255]. Immobilization vas sho vn to significantly increase stability against inactivation by aldehyde substrates [256]. The enzyme is quite tolerant to organic cosolvent, and preparative reactions have been performed continuously in a membrane reactor [255], vith potential in-situ product removal via borate complexation [257]. 

Of the enzymes listed in Table 10.1, Upases are the woikhorses. The employment of Upases in non-aqueous media is an estabUshed art, with over 25 years of research serving as a foundation. Lipases are abundant and relatively inexpensive enzymes that require no co-factors and are easily immobilized. Lipases from several thermophiUc organisms have been isolated, cloned, and mass produced via recombinant DNA technology in common vectors such as Escherichia coli. Some of the examples in Table 10.1 are surfactants formed from enzymatic hydrolysis of oleochemical feedstocks, such as MAG formed from lipase-catalyzed hydrolysis of TAG, and lysophospholipids via hydrolysis by Upases or phosphoUpase A. Ui the foUowing sections some specific examples from the literature are given of enzyme-catalyzed synthesis of bio-based surfactants. Other examples not described, such as the oxidation of fatty alcohols to aldehydes (OrUch et al., 2000) and the covalent attachment of fatty alcohols and bio-based diethyl carbonate (Banno et al., 2007, 2010 Matsumura 2002 Lee et al., 2010) are covered in the references provided. 

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