Knowledge of the role of enzymes as catalysts has grown with knowledge of catalysis in general.
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Berzelius was first who defined and recognized the nature of catalysis and proposed in 1837 that “ferments” were catalysts produced by living cells.
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Nevertheless, little was known about the chemical nature of enzymes until the beginning of this century, when there was growing conviction that enzymes were probably protein in nature.
The crystallization of urease from jack been seeds in 1926 by Sumner, pepsin from the gastric juice of the cow in 1930 by Northrop and trypsin from the pancreas of the cow in 1931 by Northrop and Kunitz showed that enzymes are infact proteins.
Over 1000 enzymes of all classes are now identified and about 150 have been crystallized and purified (Northrop, 1948., Florkin and Stolz, 1964; Lehninger, 1970).
So all enzymes isolated so far are proteins, out of which many are conjugted proteins in their chemical nature.
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They have the same properties and characteristics as proteins have in general. The clear evidences for the protein-like characters of enzymes are the colloidal nature of these biochemical catalysts, colour reactions, ultraviolet absorption spectra, inactivation by heat and radiations, and sensitivity to pH and salts, and so forth.
Enzymes form colloidal solution in water and are not soluble in high concentration of alcohol and alkaline reagents by which they are precipitated. Enzymes like proteins do not pass through a dialyzing membrane.
They migrate under the influence of an electrical current which indicates that they are protected by electrical charges.
They can be destroyed by heat, which indicates a solvent protection. Enzymes contain protein molecules which are attached with other non-protein groups such as metals, vitamins and carbohydrates depending upon the particular enzyme. These non-protein groups are called prosthetic groups.