Boron based separations for in situ recovery of L-erythrulose from transketolase-catalyzed condensation

In this article we report on the application of in situ product removal (ISPR) (the concurrent recovery of a product during the product formation process) as a means of improving the productivity of bioconversions. The Escherichia coli transketolase-catalyzed condensation of glycolaldehyde with beta-hydroxypyruvate to yield L-erythrulose (and carbon dioxide) was chosen as a model system. Those ISPR methods based on phenylboronate-diol interactions showed greatest potential for use as a selective means of removing L-erythrulose from the reaction medium. Soluble, insoluble, and immobilized boronates were investigated. Concentrations of free phenylboric acid of 100 mM and above were toxic to transketolase, thus rendering the use of these methods unsuitable for ISPR. However, one of the immobilized phenylboronate resins (Affi-Gel 601(R)) was not toxic to the enzyme, although significant levels of nonspecific binding of both substrates were observed. When ISPR was performed on the model reaction using this resin with substrate feeding, it proceeded to completion. (C) 1997 John Wiley & Sons, Inc.