Enzyme classes, major

Several classes of non-covalent substrate based inhibitors have been reported, and are grouped below based on the nature of the C-terminal group interacting with the catalytic triad of the enzyme. The majority of the reported inhibitors are based on the N-terminal product of a modified substrate of the NS5A/5B cleavage side or to a lesser extent of the NS4A/4B substrate peptide. 

Cysteine proteases are a class of enzymes that have been widely studied over the years. The overall principles of substrate recognition, catalysis, and inhibition are now reasonably well documented. This enzyme class includes the plant proteases such as papain, actinidin, and bromelain, and several mammalian lysosomal cathe-psins. By far the majority of the literature reports dealing with cysteine proteases describe results obtained with the enzyme papain, because it is considered to be the archetype of this enzyme class. 

The majority of industrial biocatalytic processes involve the use of hydrolytic enzymes including proteases, transaminases, glycosidases, aminoacylases, and lipases as well as several additional enzyme classes... 

Protein kinases catalyze the transfer of the 7-phosphate moiety of ATP to the corresponding protein substrate. More than 30% of all eukaryotic proteins are phosphorylated, with the majority of the modifications occurring on serine or threonine residues 89 Kinases constitute the largest enzyme class in eukaryotic proteomes with more than 500 members encoded in the human genome90 and play a central role in most signal transduction pathways... 

Many functions of protein kinase C in signaling pathways are closely linked with the membrane association of the enzyme. Signal-dependent association of PKC with the cell membrane is therefore another major regulatory aspect of this enzyme class. Activation of protein kinase C, initiated by addition of phorbol esters, for example, is associated with a redistribution of the enzyme from the cytosol to the membrane. 

Two major classes of reversible inhibitors can be distinguished on the basis of the sites on the enzyme to which they bind. One class consists of compounds very similar in structure to the substrate. In this case, the inhibitor can bind to the active site and block the substrate s access to it. This mode of action is called competitive inhibition because the inhibitor competes with the substrate for the active site on the enzyme. Another major class of reversible inhibitors includes any inhibitor that binds to the enzyme at a site other than the active site and, as a result of binding, causes a change in the structure of the enzyme, especially around the active site. The substrate is still able to bind to the active site, but the enzyme cannot catalyze the reaction when the inhibitor is bound to it. This mode of action is called noncompetitive inhibition (Eigure 6.11). 

A number of diverse reactions are possible by biocatalytic processes, which are catalysed by enzymes. The major six classes of enzymes and the type of reactions they catalyse are discussed as follows ... 

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