Peptide bond between amino acids

Proteases (proteinases, peptidases, or proteolytic enzymes) are enzymes that break peptide bonds between amino acids of proteins. The process is called peptide cleavage, a common mechanism of activation or inactivation of enzymes. They use a molecule of water for this, and are thus classified as hydrolases. 

How does cleavage of a single peptide bond activate the zymogen Key conformational changes, which were revealed by the elucidation of the three-dimensional structure of chymotrypsinogen, result from the cleavage of the peptide bond between amino acids 15 and 16. 

When trypsin activates chymotry psin, it cleaves chymotrypsinogen at the peptide bonds between amino acids Arg 15 and Do IB. The numbers indicate the amino acid residue sequence numbers, counting from the N-terminal end of the protein. As stated earlier, enterokinase catalyzes the activation of trypsinogen, which begins a cascade of events resulting in the activation of all the pancreatic enzymes... 

Before proteins can actively function in the living cell they must fold up into a specific 3-dimensional structure, the so-called native state (see Fig. 1). Already in the 1960 s it was recognized that the long linear polypeptides chains can adopt their native structure starting from the random coil state in a surprisingly short time. The famous Levinthal paradox states that if a peptide bond between amino acids can only adopt two conformations a relatively short protein of a hundred residues can have around 2 10 possible... 

Why is protein synthesis so different from that of polysaccharides or lipids The actual chemistry of the formation of peptide bonds between amino acids is of the type of reaction that we are already quite familiar with. Two amino acids can link together with the removal of water to form a di peptide ... 

In this chapter we consider the nucleic acids. These macromolecules (1) contain the information for determining the amino acid sequence and hence the structure and function of all the proteins of a cell, (2) are part of the cellular structures that select and align amino acids in the correct order as a polypeptide chain is being synthesized, and (3) catalyze a number of fundamental chemical reactions in cells, including formation of peptide bonds between amino acids during protein synthesis. 

Primary Structure The primary structure of the protein is the amino acid sequence of the protein. The primary structure results from the formation of covalent peptide bonds between amino acids. Peptide bonds are amide bonds formed between the a-carboxylate group of one amino acid and the a-amino group of another. 

PHARMACOKINETICS When vasopressin and desmopressin are given orally, they are rapidly inactivated by trypsin, which cleaves the peptide bond between amino acids 8 and 9. Inactivation by peptidases in various tissues (particularly the Uver and kidneys) results in a plasma tj of vasopressin of 17-35 minutes. Following intramuscular or subcutaneous injection, the antidiuretic effects of vasopressin last 2-8 hours. The plasma t of desmopressin has a fast component of 6.5-9 minutes and a slow component of 30-117 minutes. Only 3% and 0.15%, respectively, of intranasaUy and orally administered desmopressin is absorbed. 

The elongation phase of polypeptide synthesis is depicted in Fig. 9-12. The 508 subunit is a peptidyl transferase that catalyzes the formation of a peptide bond between amino acids. The 238 rRNA is responsible for this catalytic activity. As its name implies, it transfers the fMet (and in later reactions a peptide) from the tRNA that occnpies the P site to the amino acid on the tRNA in the A site. To do this, the amino group of... 

Protein digestion occurs by hydrolysis of the peptide bonds between amino acids. There are two main classes of protein digestive enzymes (proteases), with different specificities for the amino acids forming the peptide bond to be hydrolysed, as shown in Table 4.2 ... 

The formation of peptide bonds between amino acid residues, which is directed by mRNA and catalyzed by ribosomes, is at the heart of protein biosynthesis. However, a wide variety of other processes are also necessary for proteins to achieve their biological function(7, ). All polypeptides must undergo noncovalent changes, such as folding of the polypeptide chain, association with other subunits, and translocation across membranes. Many also undergo covalent modifications of both the peptide backbone and amino acid side chains. These covalent modifications can drastically affect both protein structure and function. 

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