Protein digestion peptide bonds broken

Proteolytic enzymes, such as the serine proteases, are among the best characterized of all enzymes.They are important in digestive processes because they break down proteins. They each catalyze the same type of reaction, that is. the breaking of peptide bonds by hydrolysis. The crystal structures of several serine proteases have been determined, and the mechanism of hydrolysis is similar for each. The specificity of each enzyme is, however, different and is dictated by the nature of the side chains flanking the scissile peptide bond (the bond that is broken in catalytic mechanism. Chymotrypsin is one of the best characterized of these serine proteases. The preferred substrates of chymotrypsin have bulky aromatic side chains. The crystal structure determination of the active site of chymotrypsin, illustrated in Figure 18.12, has provided much of the information used to elucidate a plausible mechanism of action of the enzyme. In the first step of any catalyzed reaction, the enzyme and substrate form a complex, ES, the Michaelis complex. The hydrolysis of the peptide bond by chymotrypsin involves three amino acid residues,... 

In all forms of digestion (whether of proteins, carbohydrates, or fats), larger molecules are broken down into smaller molecules by a reaction with water in which a water molecule is split in two, each part joining a different product molecule. This type of reaction is called hydrolysis. Remember that proteins are long chains of amino acids linked together by amide functional groups called peptide bonds. When protein molecules are digested, a series of hydrolysis reactions convert them into separate amino acids. 

Proteins in food are initially broken down into smaller polypeptides by endopeptidases that hydrolyze peptide bonds within the chain. Digestive enzymes have specificity or preference for particular side chains adjacent to the peptide to be cleaved, but there is sufficient variety to break the great majority of proteins into small polypeptides. The endopeptidases include the pepsins, trypsin, chymotrypsin, and elastase. 

Peptide bonds can be broken by enzymes called proteases. These enzymes are foimd in cells and tissues where they aid in the digestion of proteins from food, or where they degrade urmeeded or damaged proteins. 

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