He found that this enzyme consisted entirely of protein and postulated that all enzymes would consist of proteins. Many questions remain about enzymes, but the size relationship between an enzyme and its substrate remains central to understanding enzyme catalysis. A medium sized enzyme molecule has a molecular weight of about 100,000 with a diameter of 7 nm, whereas a typical substrate has a molecular weight of 250 and a diameter of 0.8 nm. Enzymes Show All The Properties of Proteins. Enzymes are inactivated by heat, extremes of pH, or other denaturing agents.
Some enzymes consist only of protein, others require an additional component called a cofactor.
These cofactors maybe inorganic such as iron, zinc, magnesium, or a complex organic molecule called a coenzyme. Some enzymes may require both a cofactor and a coenzyme. Enzymes enhance the rate of chemical reactions by lowering their activation energy, but like the catalytic agents we have studies thus far, they cannot change the equilibrium point of a reaction they promote, nor are they used up or permanently changed. Review the concept of exergonic and endergonic reactions. The concentration of the substrate has a great effect on the rate of enzyme-catalyzed reactions, and like catalytic reactions their concentration is very small in comparison to the substrate.