Cofactor regeneration could only occur if the speed of the biotransformation reaction and cofactor regeneration reaction are similar

Cofactors are essential for many oxidoreductases employed in biocatalysis, where substrates are commonly converted into enantioselective isomers of value-added products. This then necessitates the continuous provision of cofactors in support of the biotransformation, which incurs significant cost for the process. Hence, researchers in the biocatalysis field invented the approach of cofactor regeneration to help recycle the redox cofactors to help pull the biotransformation reaction forward. Redox cofactors cycle between the oxidized and reduced forms during a reaction. In cofactor regeneration, a second reaction using a cheap substrate is used to convert oxidized cofactor to the reduced form or vice versa. In this way, the cost of cofactor is shifted towards that of the sacrificial substrate used in the second cofactor regeneration reaction. While simple in conceptualization, practical implementation of the above scheme faces significant challenges. Specifically, the coupling of the cofactor regeneration reaction and the main biotransformation reaction is only possible if the speed of both reactions are similar. For example, if the cofactor regeneration reaction is faster than the biotransformation reaction, one form of the cofactor would accumulate, and the coupled system would stop functioning, leading to poor yield of product. The situation described above thus place severe constraints on the type of biotransformation reactions that could be coupled to a cofactor regeneration reaction. Naturally, a cofactor regeneration reaction is more useful if it can be coupled to more biotransformation reactions. Hence, some trial and error as well as experience in biocatalysis is needed to help make judicious choice of the biotransformation reaction for coupling with a cofactor regeneration reaction. Future work in machine learning enabled prediction of enzyme activity and reaction kinetics may go a long way in helping researchers make appropriate choices in cofactor regeneration systems selection in biocatalysis. Collectively, while conceptual underpinnings of cofactor regeneration are established, the method still faces challenges in ability to couple with diverse types of biotransformation reactions. This comes about due to the mismatch between speed of biotransformation and cofactor regeneration reaction. Hence, only particular types of biotransformation reactions can be usefully coupled to particular cofactor regeneration reaction.