Enzymes are substances produced by living cells which behave like catalysts in that they change the rate of chemical reactions without themselves undergoing any apparent physical or chemical change. Since enzymes have not been isolated in a pure state, our knowledge of their properties is limited to the study of the reactions that they accelerate or retard.
In quantitative tests of enzymatic activity, a fixed proportion must exist between the amount of enzyme that is present and the effect that is produced. It is therefore essential that the laws governing their velocity of reaction should be properly applied.
According to the law of mass action, the rate of reaction is proportional to the concentration of the reacting molecules. At any moment the velocity of reaction is proportional to the amount of substance that remains undecomposed. In a unimolecular reaction of an inorganic catalyst, such as the hydrolysis of cane sugar
HOLLANDER E, MARCUS JM. PANCREATIC FUNCTION: I. THE QUANTITATIVE DETERMINATION OF PANCREATIC ENZYMES. Arch Intern Med (Chic). 1925;36(4):585–591. doi:10.1001/archinte.1925.00120160143008
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