Globular proteins hydrolysis

Different enzymes have different specificities. Some, such as amylase, are specific for a single substrate, but others operate on a range of substrates. Papain, for instance, a globular protein of 212 amino acids isolated from papaya fruit, catalyzes the hydrolysis of many kinds of peptide bonds. In fact, it s this ability to hydrolyze peptide bonds that makes papain useful as a meat tenderizer and a cleaner for contact lenses. 

Ribonuclease, another small globular protein (Mt 13,700), is an enzyme secreted by the pancreas into the small intestine, where it catalyzes the hydrolysis of certain bonds in the ribonucleic acids present in ingested... 

Most of the machinery of living cells is made of enzymes. Thousands of them have been extracted from cells and have been purified and crystallized. Many others are recognized only by their catalytic action and have not yet been isolated in pure form. Most enzymes are soluble globular proteins but an increasing number of RNA molecules are also being recognized as enzymes. Many structural proteins of the cell also act as catalysts. For example, the muscle proteins actin and myosin together catalyze the hydrolysis of ATP and link the hydrolysis to movement (Chapter 19). Catalysis is one of the most fundamental characteristics of life. 

Enzymes, we have said, are proteins that act as enormously effective catalysts for biological reactions. To get some idea of how they work, let us examine the action of just one chymotrypsin, a digestive enzyme whose job is to promote hydrolysis of certain peptide links in proteins. The sequence of the 245 amino acid residues in chymotrypsin has been determined and, through x-ray analysis, the conformation of the molecule is known (Fig. 37.1). It is, like all enzymes, a soluble globular protein coiled in the way that turns its hydrophobic parts inward, away from water, and that permits maximum intramolecular hydrogen bonding. 

The effects of hydrolysis on surface properties depend on the type of milk protein and the conditions of hydrolysis. Hydrolysis of globular proteins results in the exposure of buried hydrophobic groups. This enhances surface hydrophobicity that improves surface properties. The degree of hydrolysis needs to be optimized for good surface properties. This is governed by the type of protein used, the extent of hydrolysis, and the enzymes used. 

Increased hydrophobicity may be achieved by enzymatic hydrolysis, which can lead to rearrangements of the buried hydrophobic groups present in the native globular protein [74], On the other hand, the opposite effect may be observed if the end products are low molecular weight segments [75], Therefore an optimum in surface activity is achieved at a specific molecular weight range for each protein [75],... 

The enzyme-catalyzed hydrolysis of a particular peptide bond is determined by two major factors, the susceptibility of that bond to the specific proteinase and the flexibility of the protein chain in the region of the bond. Thus a globular protein undergoes frequent fluctuations, and the sites of the peptide chains of highest mobility are the most susceptible to proteolytic reactions. On the other site, the... 

Ans. The HCl brings the pH of the stomach to between 1.5 and 2.0, which serves two functions. The low pH kills most bacteria, and also denatures or unfolds globular proteins which makes internal peptide bonds accessible to enzymatic hydrolysis. 

The major problem in all work carried out on isopeptides was related to the fact that the isopeptide bond is chemically an amide bond and as a consequence of this is susceptible to attack by acids or alkalis, thus destroying the isopeptide. The only possible methods were microbiological or enzymic, both of which obviate the problem of random hydrolysis. Methods of enzymic digestion had previously been knowi and adequately used however, such methods, although suitable for globular proteins, proved to... 

These proteins produce only amino acids on hydrolysis. They are subdivided into two groups, fibrous and globular proteins, according to shape, solubility and chemical composition. 

It is not always possible to apply enzymatic hydrolysis directly to proteins as they are in the native form. Native, globular proteins (e.g., from soy, corn, almond) or fibrous insoluble proteins (e.g., collagen, keratins, elastin) are generally resistant to proteolysis this is generally explained by the compact tertiary structure of the protein that protects most of the peptide bonds. In the denatured, unfolded form the peptide bonds are exposed and available for enzymatic cleavage. As native proteins in aqueous solution are in dynamic equilibrium with a number of more or less distorted forms, part of which can be considered denatured and thereby accessible to enzyme attack, the initial break of a few peptide bonds can destabilize the protein molecule and cause irreversible unfolding in some cases (e.g., hydrolysis of egg albumin by pepsin) this mechanism allows the protease to perform the hydrolysis to a remarkable extent. More frequently, especially when covalent bonds (disulfide bonds) stabilize the native form of the protein, a preliminary partial or extended denaturation is needed to make enzymatic hydrolysis possible this is normally achieved by heating or chemical attack, or a combination of the two. 

Ribbons result from the lateral stacking of fibrils. They are observed rally after a prolonged heating at acid pH of globular proteins as different as LYS or P-Lg. The formation of multistranded ribbons occurs concomitantly with an extensive hydrolysis of the proteins into low molecular weight peptides [23]. Such small peptides are hypothesised to be responsible for the formation of multistranded ribbons. 

Chemical reactions between biochemical compounds are enhanced by biological catalysts called enzymes, which consist mostly or entirely of globular proteins. In many cases a cofactor is needed to combine with an otherwise inactive protein to produce the catalytically active enzyme complex. The two distinct varieties of cofactors are coenzymes, which are complex organic molecules, and metal ions. Enzymes catalyze six major classes of reactions 1) Oxidoreductases (oxidation-reduction reactions), 2) Transferases (transfer of functional groups), 3) Hydrolases (hydrolysis reactions), 4) Lyases (addition to double bonds, 5) Isomerases (isomerization reactions) and 6) Ligases (formation of bonds with ATP (adenosine triphosphate) cleavage) [1]. 

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