**1. Introduction**

Biocatalysis is appropriately defined as the enzyme-based applications for the transformation of molecular substrate into several natural as well as synthetic chemicals [1, 2]. The enzymes used in the process are in the form of cell lysate, whole cells, or purified enzyme and are prepared either as recombinant expressed proteins in different host cells or expressed in their native cells itself [3]. The key players of biocatalysis are biocatalysts or enzymes that have been divided into six classes by the IUPAC nomenclature system based on the reactions they catalyze [4], as shown in **Table 1**.

Enzymes as biocatalysts are incredibly proficient and are always preferred to conventional chemical processes. It is due to the fact that enzyme-based biocatalysis has distinct advantages over chemical reactions such as (1) significant specificity towards catalyzed reactions and recognized substrates, (2) simplified synthetic route, (3) high yields with exceptional regio-, chemo-, and stereoselectivities, (4) minimum energy requirements, and (5) generation of less by-products and wastes [5–8]. Another preferred advantage includes whole bioprocess and bulk operations being carried out under mild conditions at elevated rates and with extreme specificity and with minimum environmental and physiological toxicity, thus making them an ideal candidate in the development and improvement of sustainable chemical processes [9–12].


#### **Table 1.**

*IUPAC classification of enzymes based on reactions they catalyze.*

However, despite holding tremendous potential, biocatalysis has an inevitable pitfall associated with it when extreme conditions of industrial processes are to be considered. An efficient biocatalyst needs to be compatible enough with specific properties such as thermostability, catalytic ability, substrate specificity, and operational stability in turbulent flow regimes, toxic, hazardous solvents, and substrate inhibition [13–21].

Thus, there is a need for the identification and production of stable biocatalysts with broad industrial applicability by exploring and screening novel microbes or identification of new genes with desired properties through the analysis of genes responsible for enzyme production and stability. Further enhancement of the enzyme properties can be done by applying protein engineering tools such as molecular docking, directed evolution, molecular modeling, and process engineering [22–25].
