Amino acids bonding between

The similarity of the primary structure of different sea snake venoms has already been discussed. Postsynaptic neurotoxins from Elapidae venom have been extensively studied. Elapidae include well-known snakes such as cobra, krait, mambas, coral snakes, and all Australian snakes. Like sea snake toxins, Elapidae toxins can also be grouped into short-chain (Type I) and long-chain (Type II) toxins. Moreover, two types of neurotoxins are also similar to cardiotoxins, especially in the positions of disulfide bonds. However, amino acid sequences between cardiotoxins and sea snake and Elapidae neurotoxins are quite different. In comparing the sequence of sea snake and Elapidae neurotoxins, there is a considerable conservation in amino acid sequence, but the difference is greater than among the various sea snake toxins. 

Insulin has 51 amino acids, divided between two chains. One of these, the A chain, has 21 amino acids the other, the B chain, has 30. The A and B chains are joined by disulfide bonds between cysteine residues (Cys-Cys). Figure 27.10 shows some of the information that defines the amino acid sequence of the B chain. 

Identity of amino acid sequences between subtilisins E and BPN is 86%, so three-dimensional structures of the two enzymes are considered to be very similar. In the case of subtilisin BPN, residues 61 and 98 are located on the loop and turn structure, respectively, both of which connect /3-strand and a-helix (Fig. 12.5). Solvent exposures of the residues are both 9,45) indicating their presence on the surface of the enzyme molecule. The distance between the a-carbons of the two residues is 5.8 A. Accordingly, the positions seem appropriate for cysteine residues to form a disulfide bond without any strain in the enzyme structure. The disulfide bond formed is located close to the active site so as to stabilize the wall of the active-site pocket (Fig. 12.5). 

Some of these sites can effect function in zinc proteins as well as stabilizing structure. The hydrolase class of zinc enzymes are good examples of this action. In this case, one or more amino acid residues within the active site may be provided by the amino acid spacers between zinc ligands (Figure 12). The side chain of these amino acids may be involved in substrate binding, bond cleavage or modulating the chemical enviromnent of the active site. In addition, other active-site residues are often provided by... 

The first study compared PA-EC with PA-AF [12]. The mutation of S67A in one part of the active site leads to weaker interactions with H-bonding probes in PA-AF. Several other amino acid differences between the enzymes translate into different interaction strengths or even structural differences of the protein backbone, which are reflected in the shape of the MIFs and the interaction energy maxima. Together with docking calculations of model substrates, the authors were able to explain the experimental selectivity profile and the enantioselectivity of the enzymes. 

Proteins are constructed from amino acids which are assembled by the formation of peptide bonds. The amino group of one amino acid bonds with the carboxyl group of another, eliminating one water molecule (HOH). The bond between the two amino acids consists of a nitrogen with one hydrogen bonded to a carbon with a double-bonded oxygen H-N-C=0. 

C) Tertiary structure is formed by hydrophobic and electrostatic interactions between amino acids, and by hydrogen bonds between amino acids and between amino acids and water. 

Vasotab, a vasoactive 56-peptide from horse fly Hybomitra bimaculata (Diptera, Taban-idae) salivary glands. The peptide contains six cysteine residues which form three disulfide bonds similar to the disulfide pattern of the Kazal-type protease inhibitors. In comparison to the latter, vasotab has an unique 7-amino-acid insertion between the third and fourth cysteine residues within the peptide chain. Vasotab shows positive inotropism in isolated rat hearts, vasodilatation of coronary and peripheral vessels, and Na+/K+-ATPase inhibition. Furthermore, it is capable of blocking L-type calcium channels [P. Takac et al., J. Exp. Biol. 2006, 209, 343]. 

A subsequent study reported on a number of SDH variants where amino acids situated between the Mo and heme cofactors (particularly R55) were shown to play a crucial role in catalysis. The crystal structure of SDH (Figure 5.7) defines the key position of R55 and H57 and how the former forms H-bonds to the Mo and heme cofactors simultaneously. 

Amino acids bond to each other by forming a peptide bond, an amide group formed by a condensation reaction between the carboxyl group of one amino acid and the amino group of another. Two amino acids linked by a peptide bond form a dipeptide. A chain of two or more amino acids linked by peptide bonds is called a peptide. The term polypeptide is applied to a chain of ten or more amino acids. Proteins may have one or several polypeptide chains, and each chain must have an exact sequence of amino acids. 

The only consistent difference observed between the effects of the two enzymes appears to be a smaller effect of chymotrypsin on electron-transport and phosphorylation. This difference may be due to a lack of availability of the specific amino acid bonds which chymotrypsin attacks. 

Proteins are biopolymers formed by one or more continuous chains of covalently linked amino acids. Hydrogen bonds between non-adjacent amino acids stabilize the so-called elements of secondary structure, a-helices and / —sheets. A number of secondary structure elements then assemble to form a compact unit with a specific fold, a so-called domain. Experience has shown that a number of folds seem to be preferred, maybe because they are especially suited to perform biological protein function. A complete protein may consist of one or more domains. 

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