Polypeptides bonding

Through the formation of polypeptide bonds between amino acids, very long chains of sequences are obtained. Generally, proteins consist of hundreds and thousands of amino acids. For example, human hemoglobin has four polypeptide chains, of which two are cf-chains and two are j3-chains. There are 141 amino acids in each a-chain with a sequence of... 

If the number of amino acids forming polypeptide bonds is more than 12.000, the polypeptides are called PROTEINS. 

These are polyamides and the monomers from which they are derived are a-amino carboxylic acids. They are found in all living cells. These compounds contain more than 12000 polypeptide bonds. 

TTie key factor that sets enzymatic reactions apan from other catalyzed reactions is the formation of an enzyme-substrate complex, E S. Here substrate binds with a specific aaive site of the enzyme to form this complex. Figure 7-5 shows the schematic of the enzyme chymolrypsin (MW 25,000 Daltons), which catalyzes the hydrolytic clearage of polypeptide bonds. In many cases the enzyme s active catalytic sites are found where the various folds or loops interact. For chymoUy psin the catalytic sites are noted by the amino acid numbers 57, 102, and 195 in Figure 7-5. Much of the catalytic power is attributed... 

Through the formation of polypeptide bonds between amino acids, very long chains of sequences are obtained. Generally, proteins consist of... 

After cross-linking, the experimenter analyzes the solution on an SDS gel. Thick gels (3 to 1.5 mm instead of 0.75 mm) allow us to load a lot of protein per pocket and thus enhance the signal of the ligand/binding polypeptide bond in the autoradiogram or fluorogram. 

There are probably however, in proteins other types of bonds apart from the polypeptide bond. An argument in favour of this is that the enzyme pepsin can destroy proteins but not polypeptides. 

Some of the proteins involved in the formation of the polypeptide bond have now been identified. 

The names of many great chemists are associated with the study of proteins. The famous organic chemist Baron Justus von Liebig maintained for a long time that all proteins stemmed from only one type of molecule, and all variations had the same radical. But the composition of these large molecules was to remain mysterious until Emil Fisher established that proteins were made of up to 20 different amino acid residues linked by polypeptide bonds. 

To understand the resonance of the peptide bond, consider first the two extreme forms in which this double bond may exist the covalent and the ionic. In active polypeptide bonds, neither the covalent nor the ionic form exists, but the two types form a resonating unit, as is expected from the resonance theory. 

The activation of chymotrypsinogen to chymotrypsin involves splitting a polypeptide bond somewhere between the first and the fifteenth amino acid in the N-terminal sequence. As was the case for trypsinogen, the activation involves the rupture of an isoleucyl bond. In fact, in the activation of both trypsinogen and chymotrypsinogen, the first accessible bond in... 

Specifie epiphytie mieroflora typieal of this partieular fiber is always present on its snrface. Representatives of this mieroflora excrete proteolyric enzymes (mostly pepsin), which induce hydrolytie keratine deeay by polypeptide bonds to separate amino acids. 

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