Rules for biocatalyst and reaction engineering to implement effective, NAD(P)H-dependent, whole cell bioreductions.
Access to chiral alcohols of high optical purity is today frequently provided by the enzymatic reduction of precursor ketones. However, bioreductions are complicated by the need for reducing equivalents in the form of NAD(P)H. The high price and molecular weight of NAD(P)H necessitate in situ recycling of catalytic quantities, which is mostly accomplished by enzymatic oxidation of a cheap co-substrate. The coupled oxidoreduction can be either performed by free enzymes in solution or by whole cells. Reductase selection, the decision between cell-free and whole cell reduction system, coenzyme recycling mode and reaction conditions represent design options that strongly affect bioreduction efficiency. In this paper, each option was critically scrutinized and decision rules formulated based on well-described literature examples. The development chain was visualized as a decision-tree that can be used to identify the most promising route towards the production of a specific chiral alcohol. General methods, applications and bottlenecks in the set-up are presented and key experiments required to "test" for decision-making attributes are defined. The reduction of o-chloroacetophenone to (S)-1-(2-chlorophenyl)ethanol was used as one example to demonstrate all the development steps. Detailed analysis of reported large scale bioreductions identified product isolation as a major bottleneck in process design.
Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 12/I, 8010 Graz, Austria. Electronic address: regina.kratzer@tugraz.at.
Regina
R
Kratzer
CAPEC-PROCESS Research Center, Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads Building 229, 2800 Kgs. Lyngby, Denmark. Electronic address: jw@kt.dtu.dk.
John M
JM
Woodley
Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 12/I, 8010 Graz, Austria. Electronic address: bernd.nidetzky@tugraz.at.
Bernd
B
Nidetzky
D000438:Alcohols / Q000737:chemistry*; D055162:Biocatalysis; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D007659:Ketones / Q000737:chemistry; D060847:Metabolic Engineering; D009249:NADP / Q000737:chemistry; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000737:chemistry* / Q000235:genetics; D013379:Substrate Specificity; D002721:omega-Chloroacetophenone / Q000737:chemistry
D000438:Alcohols; D007659:Ketones; D009249:NADP; D002721:omega-Chloroacetophenone; D010088:Oxidoreductases
Chiral alcohol; Cost analysis; Decision tree for bioreduction development; Design of Escherichia coli whole cell catalysts; Limitations of whole cell reductions; Scale-up