Protease digestion

Figure 2.14 shows examples of both cases, an isolated ribbon and a p sheet. The isolated ribbon is illustrated by the structure of bovine trypsin inhibitor (Figure 2.14a), a small, very stable polypeptide of 58 amino acids that inhibits the activity of the digestive protease trypsin. The structure has been determined to 1.0 A resolution in the laboratory of Robert Huber in Munich, Germany, and the folding pathway of this protein is discussed in Chapter 6. Hairpin motifs as parts of a p sheet are exemplified by the structure of a snake venom, erabutoxin (Figure 2.14b), which binds to and inhibits... 

H-gal-GP 35 to 230 (unreduced) Digestive protease complex Suffolk Cross 93 72 Smith etal., 1994 Smith and Smith, 1996... 

Inactivation due to digestive proteases. Therapeutic proteins would represent potential targets for digestive proteases such as pepsin, trypsin and chymotrypsin. 

Chen, Z. and L.M. Mayer. 1998. Digestive proteases of the lugworm (Arenicola marina) inhibited by Cu from contaminated sediments. Environ. Toxicol. Chem. 17 433-438. 

R. B. Van Breemen, M. G. Bartlett, Y. Tsou, C. Culver, H. Swaisgood, S. E. Unger, Degradation of Peptide Drugs by Immobilized Digestive Proteases , Drug Metab. Dispos. 1991, 19, 683-690. 

Many proteins are formed as inactive precursors and become activated by proteolysis. The inactive precursors are termed proenzymes, zymogens or - for hormones like e.g. insulin - prehormones. Processing to the active form occius in a cell- and tissue-specific way and usually requires a specific protease. Activation can also occur intramolecu-larly by autoproteolysis. In most cases, short sequences of the protease substrate serve as a recognition signal for the attack of the processing protease. Of the numerous examples of proteolytic processing of proteases only the digestive proteases will be discussed in more detail. 

Different enzymes are used for digestion. Proteases are the most widely used group of enzymes. The most commonly used proteases are... 

Garcfa-Carrefio, F.L. 1992. The digestive proteases of langostilla (Pleuroncodes planipes, De-capoda) Their partial characterization, and the effect of feed on their composition. Comp. Biochem. Physiol. l03B 575-578. 

Pis inhibit the digestive protease enzyme of HIV, which it uses to break the proteins of healthy cells into smaller pieces. These infected smaller pieces of protein then carry on infecting new host cells. Pis therefore slow down HIV proteases and subsequently inhibit the infection of new cells [94]. 

Pallares I et al (2008) Direct interaction between a human digestive protease and the mucoadhesive poly(acrylic acid). Acta Cryst Sect D 64 784-791 PDBID 2V77... 

The destructive potential of proteases means that their activity has to be tightly regulated to prevent autolysis of protease-producing cells. Thus digestive proteases such as chymotrypsin, pepsin and trypsin are produced as inactive zymogens (proenzymes) and are subsequently activated after secretion. The serine protease-catalysed process of blood clotting involves a cascade of successive proteolytic activations of the blood clotting factor proteases involved [2-6]. 

Many of the digestive proteases are produced and secreted as inactive zymogens. They are converted to their active forms by removal of a peptide fragment in the lumen of the digestive tract. 

Human serum Enzymatic digests (protease) analyzed... 

See Section 20.11 and Figure 20.12 for a more detailed picture of the action of digestive proteases. 

Proteins are amino acids linked tfirough peptide bonds. Dipeptides fiave two amino acids, tripeptides fiave tfiree amino acids, and so on. Digestive proteases are enzymes tfiat cleave the peptide bonds between the amino acids (see Chap.1, Fig. 1.5). 

Proteolytic enzymes (also called proteases) break down dietary proteins into their constituent amino acids in the stomach and the intestine. Many of these digestive proteases are synthesized as larger, inactive forms known as zymogens. After zymogens are secreted into the digestive tract, they are cleaved to produce the active proteases. 

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