11th Class Biology Biomolecules / जैव-अणु History Of Cellular Enzymes

Enzymes (Gk. en = in; zyme = yeast) are proteinaceous substances which are capable of catalysing chemical reactions of biological origins without themselves undergoing any change. Enzymes are biocatalysts. An enzyme may be defined as "a protein that enhances the rate of biochemical reactions but does not affect the nature of final product". Like the catalyst the enzymes regulate the speed and specificity of a reaction, but unlike the catalyst they are produced by living cells only. All components of cell including cell wall and cell membrane have enzymes.

Maximum enzymes (70%) in the cell are found in mitochondrion. Enzymes are also called 'biological middle man'. The study of the composition and function of the enzyme is known as enzymology.

The term enzyme (meaning in yeast) was used by Willy Kuhne (1878) while working on fermentation. At that time living cells of yeast were thought to be essential for fermentation of sugar. Edward Buchner (1897), a German chemist proved that extract zymase, obtained from yeast cells, has the power of fermenting sugar (alcoholic fermentation). Zymase is complex of enzymes (Buchner isolated enzyme for the first time).

Later J.B. Sumner (1926) prepared a pure crystalline form of urease enzyme from Jack Bean (Canavalia ensiformis) and suggested that enzymes are proteins. Northrop and Kunitz prepared crystals of pepsin, trypsin and chymotrypsin Arber and Nathans got noble prize in 1978 for the discovery of restriction endonucleases which break both strands of DNA at specific sites and produce sticky ends. These enzymes are used as microscissors in genetic engineering.