chem.qmul.ac.uk/iubmb/enzyme/), enzymes are classified into six main classes: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. Hence, lipases are hydrolases. Aldol condensation, on the other hand, is carried out by lyases, aldehyde-lyases has been assigned the number 4.1.2 (Nomenclature Committee of IUBMB, 1992). However, lipases have now been shown to catalyze not only aldol condensation, but also the Mannich reaction, Michael addition, Morita–Baylis–Hillman reaction as well (Hult and Berglund, 2007, Kapoor and Gupta, 2012, Lai et al., 2010 and Li et al., 2008)! So, to start with we have a problem with

the classification. Khersonsky and Tawfik (2010) have made some suggestions in the regard. In many cases, these Bcl-2 inhibitor promiscuous reactions involve high catalytic efficiency which is in the same range as seen in

normal enzyme catalyzed reactions. Babtie et al. (2010) have discussed this and point out that rate accelerations (kcat/Km)/k2 of up to 1018-fold are known. In many other cases, protein engineering and directed evolution has been successfully used to induce catalytic promiscuity ( Khersonsky and Tawfik, 2010). Many of these reactions are industrially important. Large number of reports regarding catalytic promiscuity deal with reactions carried out with industrial preparations of lipases ( Busto et al., 2010 and Kapoor and Gupta, 2012). While catalytic promiscuity involves the active site of the enzyme, moonlighting Ceritinib concentration by proteins can involve different parts of the enzyme molecule (Jeffery, 1999). The phenomenon of moonlighting constitutes a definite shift from the well-known one gene-one protein-one function paradigm. The different functions of a moonlighting protein can be displayed: Endonuclease in two different locations in the cell (one can be even intracellular and another extracellular); by a change from the monomer to oligomer structure, in different cell

types or even with a change in ligand or substrate concentrations (Jeffery, 2009). While few examples of moonlighting involve different catalytic activities, in larger number of cases the different activities encompass non-catalytic functions like repressor, growth factor, receptor, inhibitor, chaperone and regulator activities (Jeffery, 1999, 2009). Apparently new enzymes continue to evolve. Atrazine chlorohydrolase (which degrades herbicide atrazine) has evolved (from melamine hydrolase) between 1950 and 1990 (Janssen et al., 2005). Directed evolution, of course, is being extensively used to obtain enzymes which tailored specificity (Arnold and Georgiou, 2003a and Arnold and Georgiou, 2003b). All the different phenomena and observations discussed in this section have a common message: old classification and old way of reporting data on enzyme catalyzed reactions may not be adequate. In some cases, a little tweaking of guidelines may work. Eventually, we would need to evolve new guidelines (see also Tipton et al., 2014).