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Inhibitors that occupy the active site and prevent a substrate molecule from binding to the enzyme are said to be active site-directed (or competitive , as they 'compete' with the substrate for the active site).
In chemistry, rates are normally measured in terms of rate of change of concentration, with units like mol dm -3 s -1 (moles per cubic decimetre per second). Biochemists often quote it in terms of the number of molecules of substrate which a single molecule of enzyme is processing per unit time - per second, for example. It is easier to visualise, but involves a messy calculation to get there. That's not our problem for this topic!
Conversely, some enzymes display enzyme promiscuity , having broad specificity and acting on a range of different physiologically relevant substrates. Many enzymes possess small side activities which arose fortuitously (. neutrally ), which may be the starting point for the evolutionary selection of a new function.  
Covalent catalysis involves the substrate forming a transient covalent bond with residues in the enzyme active site or with a cofactor. This adds an additional covalent intermediate to the reaction, and helps to reduce the energy of later transition states of the reaction. The covalent bond must, at a later stage in the reaction, be broken to regenerate the enzyme. This mechanism is utilised by the catalytic triad of enzymes such as proteases like chymotrypsin and trypsin , where an acyl-enzyme intermediate is formed. An alternative mechanism is schiff base formation using the free amine from a lysine residue, as seen in the enzyme aldolase during glycolysis .
Bacteria / Yeast
Autoimmune / Neuro Cond.
Heart/ Vascular Health