Enzyme Catalysis

Enzymes are complex nitrogenous organic compounds produced by living plants and animals. They are protein molecules of high molecular mass that form colloidal solutions in water, and they are remarkably effective catalysts — driving the countless reactions that sustain life. Because they run biological reactions, they are called biochemical catalysts and the phenomenon biochemical catalysis. Many enzymes have been isolated in pure crystalline form, and the first was synthesised in the laboratory in 1969.

Some enzyme-catalysed reactions

• Inversion of cane sugar by invertase:

• Glucose to ethyl alcohol by zymase:

• Starch to maltose by diastase:

• Maltose to glucose by maltase:

• Urea to ammonia and $CO_2$ by urease:

In the stomach pepsin breaks proteins into peptides, while in the intestine pancreatic trypsin hydrolyses proteins to amino acids; and milk sets into curd through lactobacilli. A summary of important enzymatic reactions is given below:

Characteristics of enzyme catalysis

• Highly efficient: one enzyme molecule may transform about a million reactant molecules per minute.
• Highly specific: each enzyme catalyses only one reaction — urease hydrolyses only urea, no other amide.
• Optimum temperature: activity peaks at a definite temperature (range 298–310 K) and falls on either side; the human body temperature of 310 K suits enzyme reactions.
• Optimum pH: activity is maximum at a particular pH, usually 5–7.
• Activators and co-enzymes: a small non-protein co-enzyme (e.g. a vitamin) or metal-ion activators such as $Na^+$, $Mn^{2+}$, $Co^{2+}$, $Cu^{2+}$ boost activity — for example amylase is very active with $Na^+$ from sodium chloride.
• Inhibitors and poisons: substances that bind the enzyme's active groups can reduce or destroy activity; many drugs work as enzyme inhibitors.

Mechanism of enzyme catalysis …