Protease hydrolyzes

Several different types of proteases hydrolyze intact storage proteins first into large fragments and then into smaller peptides and amino acids within the protein body. The peptides are transported to the cytosol where other enzymes, e. g. amino-peptidases, carboxypeptidases, dipeptidases and tripeptidases, cleave them and eventually form a pool of free amino acids [11]. 

Enzymes that act on peptide bonds (i.e., peptidases and proteases) hydrolyze peptide bonds in peptides and proteins. We examine first their classification before outlining their localizations and some physiological roles. 

Serine proteases, hydrolyzing a peptide bond Nucleophile 1st NH 2nd NH 3rdNH NH OH ... 

He, H. L., Chen, X. L., Sun, S. Y., Zhang, Y. Z., and Zhou, . C. (2006). Analysis of novel angiotensin-I-converting enzyme inhibitory peptides from protease-hydrolyzed marine shrimp Acetes chinensis. ]. Pept. Sci. 12, 726-733. 

Matsufuji, H., Matsui, T., Seki, E., Osajima, K., Nakashima, M., and Osajima, Y. (1994). Angiotensin I-converting enzyme inhibitory peptides in an alkaline protease hydrolyzate derived from sardine muscle. Biosci. Biotechnol. Biochem. 58, 2244-2245. 

A protease hydrolyzes a peptide bond. Proteases have varying degrees of specificity, depending on the chemical nature of the R group and the location of the peptide linkage. Exopeptidases attack one or both ends of a polypeptide chain, and endopeptidases attack interior linkages. 

HIV protease hydrolyzes multiprotein peptides, and the leads for HIV protease inhibitors were polypeptides. It is natural that HIV protease inhibitors still bear a resemblance to a polypeptide. Successful development of Pis required liberal use of peptidomimetic strategies to create orally available drugs. 

Aspartic proteases hydrolyze the amide bond as a result of concerted effort by an aspartic acid and an aspartate (Box 13). The aspartic acid protonates and activates the peptide A (Scheme 3.5.2) towards nucleophilic attack, and the aspartate is re-... 

As reported for Antarctic seawaters (e.g., Christian and Karl 1995 Becquevort and Smith 2001), protease activity was 2-3 orders of magnitude higher than that of /(-glucosidasic activity in all bioassays. Interestingly, the ratio of protease to /(-glucosidasic activities increased in HFe bioassays, mostly due to increase of protease activity. Proteases hydrolyze peptides and proteins, which comprise a part of the utilizable fraction of the marine organic N pool (Kirchman 2000). Consequently, the decrease of elemental organic composition (C/N ratio) observed in HFe conditions could induce protease production. 

Cysteine proteases hydrolyze protein amide bonds through formation of a thio-ester bond with an active site cysteine thiol. Cathepsin K is a member of the pa-... 

Thermolysins (Thermostable neutral proteinase ) Bacillus caldolyticus, sp., stearother-mophilus, thermoproteolyti- Extracellular, thermostable, digestive bacterial proteases. Hydrolyze the N-terminal side of hydrophobic residues. Xaa Eeu > Xaa Phe 53-56... 

Ubiquitin binding domain, which binds mono- or poly-ubiqitin Ubiquitin-specific protease, hydrolyzes both linear and branched Ub modifications Uridine diphosphate Uridine monophosphate... 

Fiq. 4. Hydrolysis of casein by several proteinases. I. Hydrolysis of casein by trypsin (A), chymotrypsin (Q), or subtilisin ( ) followed by S. griseus protease (O)- Curves B, C, and D indicate the extent of hydrolysis by individual enzymes without addition of S. griseus protease. Curve A indicates the extent of hydrolysis when S. griseus protease is added to the hydrolyzate of one of the other proteinases after approximately 47 hr. II. Hydrolysis of casein by S. griseus protease followed by hydrolysis with trypsin, chymotrypsin, subtilisin, or pepsin. The latter enzymes were added to the protease hydrolyzate after approximately 47 hr. From Nomoto et al. (1960a,b). 

Another interesting antibiotic constmct is a peptide-conjugated form of j8-KDO. jS-KDO is an inhibitor of the CMP-KDO synthetase that is involved in lipopolysaccharide (LPS) synthesis, a major constituent of the bacterial cell wall. Antibacterial activity is thus accomplished by interference with cell wall construction. /3-KDO is incapable of membrane permeation, and therefore is not useful as an antibiotic in its native form. Hammond et al. have shown that conjugation of a /3-KDO analog to certain dipeptides resolves this problem [184] (O Fig. 14). Attachment of the /3-KDO analog to a dipeptide allows the glycopeptide constmct to permeate the bacterial membrane. Inside the cell, proteases hydrolyze the peptide and release the inhibitor, resulting ultimately in bacterial cell death. 

Goldstein, S.M., Leong, J. and Bunnett, N.W. (1991). Human mast cell proteases hydrolyze neurotensin, kinetensin and Leu5-enkephalin. Peptides 12, 995-1000. 

An iniponani propeny of enzymes is that they are specific that is. one enzyme can usually catalyze only one type of reaction. For example, a protease hydrolyzes only bonds between specific amino acids in proteins, an amylase works on bonds between glucose molecules in starch, and lipa.se attacks fats, degrading them to fatty acids and glycerol, Con.sequently, unwanted products are easily controlled in enzyme-catalyzed reactions. Enzymes are produced only by living organisms, and commercial enzymes are generally produced by bacteria. Enzymes usually work (i.e., catalyze reactions) under... 

Howell and Velicangil43 44 have developed a "self-cleaning" membrane by attaching food-grade proteases onto UF membranes. The enzyme protease hydrolyzed fouling proteins, thereby increasing the permeability of the gel layer. 

The release of T3 and T4 from thyroglobulin is controlled by thyroid-stimulating hormone (TSH) from the anterior pituitary. TSH stimulates the endocytosis of thyroglobulin to form endocytic vesicles within the thyroid acinar cells (see Fig. 43.10). Lysosomes fuse with these vesicles, and lysosomal proteases hydrolyze thyroglobulin, releasing free T4 and T3 into the blood in a 10 1 ratio. In various tissues, T4 is deiodinated, forming T3, which is the active form of the hormone. 

Enzymes are added to detergents to deal with specific types of clothing stains. Proteases hydrolyze protein-based stains, and amylases convert starch-based stains to soluble materials that are easily washed away. 

Other enzymes could be utilized if the vegetable matrix is non-oleaginous, as protease hydrolyzes com gluten meal allowing the extraction of lutein, zeaxanthin and p-cryptoxanthin [81], and pectinases and cellulases to degrade cell wall polysaccharides from tomato skins to obtain more yields of lycopene in the extraction with hexane [82]. 

Serine proteases such as proteinase K, subtilisin, a-chymotrypsin, and elastase can hydrolyze PLLA endogenously. Their substrate specificities are relatively wide among proteins that are composed of L-amino acid unit and a-amido bonds, and specific as well, for L-lactic acid unit of PLLA (PLLA, PDLA, and PDLLA) that have a-ester bond. Serine proteases hydrolyze PLLA homopolymer faster than copolymers with low such as PDLLA, poly(lactide-co-glycolide). 

Figure 4. Polyacrylamide gel electrophoresis in 0.1% SDS of a) acid protease-hydrolyzed cervical mucus in citric-phosphate buffer, pH 2.5 b) non-hydrolyzed cervical mucus and c) chymotrypsin-hydrolyzed cervical mucus in phosphate buffer, pH 7.8. The electrophoresis was performed, using 7% gel, at the current of 8 ma per tube. Proteins were stained with coomassie brilliant blue and destained in acetic methanol H20 (75 50 875).

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