Experimental investigation of fructose 1,6-diphosphate production and simultaneous ATP regeneration by conjugated enzymes in an ultrafiltration hollow-fiber reactor

Production of glucose-6-phosphate by glucokinase coupled with an ATP regeneration system

A process of glucose-6-phosphate (G-6-P) production coupled with an adenosine triphosphate (ATP) regeneration system was constructed that utilized acetyl phosphate (ACP) via acetate kinase (ACKase). The genes glk and ack from Escherichia coli K12 were amplified and cloned into pET-28a(+), then transformed into E. coli BL21 (DE3) and the recombinant strains were named pGLK and pACK respectively. Glucokinase (glkase) in pGLK and ACKase in pACK were both overexpressed in soluble form. G-6-P was efficiently produced from glucose and ACP using a very small amount of ATP. The conversion yield was greater than 97 % when the reaction solution containing 10 mM glucose, 20 mM ACP-Na₂, 0.5 mM ATP, 5 mM Mg²⁺, 50 mM potassium phosphate buffer (pH 7.0), 4.856 U glkase and 3.632 U ACKase were put into 37 °C water bath for 1 h.

Thermostable ATP regeneration system using polyphosphate kinase from Thermosynechococcus elongatus BP-1 for D-amino acid dipeptide synthesis

D-alanine-D-alanine ligase from Thermotoga maritima ATCC 43589 (TmDdl) was a useful biocatalyst for synthesizing D-amino acid dipeptides. TmDdl showed a broad substrate specificity at a high temperature; however, ATP was required for its reaction. One of the methods for an effective ATP supply was the coupling reaction with an ATP regeneration system. However, ATP regeneration systems consisted of enzymes from mesophiles and were difficult to operate at high temperatures. Therefore, an ATP regeneration system that could be used at high temperatures was desired to utilize TmDdl for the effective production of D-amino acid dipeptides. To establish a thermostable ATP regeneration system, polyphosphate kinase from a thermophile, Thermosynechococcus elongatus BP-1 (TePpk), was characterized. TePpk showed thermostability up to 70 degrees C; therefore, it was considered that a thermostable ATP regeneration system could be established using TePpk. In the coupling reaction with purified TmDdl and TePpk at 60 degrees C, the amount of ATP required for D-alanyl-D-alanine synthesis could be reduced to 1% of the theoretical amount required when there was no ATP regeneration. When the coupling reaction was applied to a resting cell reaction, ATP was regenerated from an adenosine scaffold in the cell, and D-alanyl-D-alanine was successfully synthesized in the maximum yield of 80% (mol/mol) without the addition of ATP. Thus, an effective synthesis of D-amino acid dipepitides was achieved using the thermostable ATP regeneration system.

Membrane-assisted extractive bioconversions

This chapter summarizes the use of membrane reactors in extractive bioconversions as process integration systems leading to in situ product recovery. Several membrane reactor configurations are analyzed, taking into account the type of bioconversion, biocatalyst type and location (either in the aqueous phase or in the membrane), membrane chemistry and morphology, solvent (extractant) type and its biocompatibility. Modeling of liquid-liquid extractive membrane bioreactors operation is also analyzed considering kinetics and mass-transfer aspects. The chapter includes examples from the authors' laboratory as well as other published in the field. Both enzyme and whole cell-based bioconversions are considered. Relevant aspects related to the solvent (extractant) toxicity and how the membrane could protect the biocatalytic activity are analyzed. Trends in this field are also given.

Theoretical investigation of fructose 1,6-diphosphate production and simultaneous ATP regeneration by conjugated enzymes in an ultrafiltration hollow-fiber reactor

The performance of an ultrafiltration hollow-fiber reactor, in which enzymatic synthesis of fructose 1,6-diphosphate (FDP) from glucose and enzymatic ATP regeneration are performed simultaneously, was analyzed theoretically. The reaction system consists of three-step synthetic reactions catalyzed by glucokinase (GK), phosphoglucose isomerase and phosphofructokinase, and the ATP regeneration reaction catalyzed by acetate kinase. Based on a simple analytical model developed previously in which the liquid flowing in a tube was assumed to be plug flow and the radial concentration gradients in the tubes and shell side space were both neglected, a computer program was developed to calculate the concentration profiles of all the components along the flow direction in the tubes and shell side space of the reactor. From the FDP concentrations at the reactor outlet calculated under various operational conditions, reactor performances such as the FDP yield and the ATP recycle number were determined. The calculation showed the interesting phenomenon that under some conditions the FDP yield was higher when GK concentration was lower.