Amino add residues

In the case of cooperative processes, the formation of a nucleus, already discussed from the kinetical point of view, plays a crucial role. The steady state described by Eq. (1) depicts the formation of a triple helix as the simplest model by the formation of a nucleus Hx through fast pre-equilibria and subsequent propagation steps, Hx in this case is a triple-helical intermediate with x tripeptide units (that means x hydrogen bonds) in the helical state. The final product H3n 2 possesses two hydrogen bonds less than tripeptide units because the three single chains are staggered at one amino add residue each. 

Position of amino add residue and charac- teristics Human Carp Trout IV Trout I Aquatic frog Xenopus Tadpole of Xenopus Terrestrial frogs Tadpole of R. cates-beiana Shark Hetero- dontus portus- jacksoni) Lungfish (Lepido- siren paradoxa)... 

Although it is a general rule to operate at high dilution (10-4-10 5M) in oxidative folding reactions to avoid formation of intermolecular disulfide-bonded species, p.-conotoxin GIIIB offers an opposite example (Scheme 10). This toxin belongs to a family of conotoxins from marine snails consisting of 22 amino add residues with three intramolecular disulfide bonds.185 ... 

In RPC separation of peptides, the fundamental structural properties of the amino adds within the sequence and the relative accessibility of the nonpolar amino add residues to a large measure determine the overall selectivity that can be achieved with a defined RPC systemJ20-23 As a consequence, peptides typically elute from RPC sorbents in the order of their relative hydrophobicities, for a pre-selected mobile-phase composition, pH, and temperature. However, the relative hydrophobicities of different peptides are also conditional on the solvation environment in which they are placed. The exposure or greater accessibility of previously sequestered polar or hydrophobic amino acid side chains in polypeptides with well-developed secondary structures will thus significantly affect the relative binding affinities of these peptides to hydrocarbonaceous-bonded phase surfaces. 

Phenyl azides (azidoarenes), introduced by Knowles and co-workers,[8 9] are the most abundantly used class of photophores. Examples include 4-azidophenylalanine (1) and 4-azido-3-nitrophenylalanine (4) (Scheme 1). Irradiation (<300 nm) of phenyl azide (13) generates nitrene 14, electrophilic in nature, which prefers insertion into O—H and N—H bonds over C—H bonds. Nitrenes are considerably less reactive and, therefore, more selective than carbenes. Nevertheless, due to their short life span (0.1-1 ms) they react indiscriminately with virtually any amino add residue in the target protein.1101 Intramolecular rearrangements do not compete effectively with intermolecular proton abstraction and insertion reactions (Scheme 4). 

Many of the biologically active zinc metalloproteins contain a zinc(II) ion bound to one or more imidazole ligands of the amino add residue histidine. For this reason a large number of studies over an extended period have been carried out on zinc and cadmium complexes of imidazole, substituted imidazoles, histidine and related ligands. There has also been much recent activity in this field much structural information is available. 

Bronsted acid/base catalysis is the most common enzymatic mechanism, since nearly all enzymatic reactions involve a proton transfer. This means that nearly all enzymes have acidic and/or basic groups in their active site. In add catalysis, the substrate is protonated by one of the amino add residues at the active site (typically aspartic acid, glutamic acid, histidine, cysteine, lysine, or tyrosine). This residue itself must therefore be protonated at the readion pH (typically between pH 5 and 9), with a pKa just above this value. Conversely, in base catalysis, the pJCa of the deprotonating residue must be just below the physiological pH. Some enzymes can even carry out bifunctional catalysis, by protonating and deprotonating two different sites on the same substrate molecule simultaneously. 

The amino add sequence of glycyl endopeptidase was published by Ritonja et al. [45] (Fig. 1). The enzyme exists as a single unglycosylated polypeptide of 216 amino add residues (Mr 23.313). Glycyl endopeptidase is clearly a member of the papain family of cysteine proteinases [46], The three-dimensional structure... 

Stem bromelain has a broad substrate specificity, dose to the specificity of ficin (EC 3.4.22.3), end hydrolyzes a great variety of synthetic and natural substrates. It preferentially cleaves peptide bonds when a hydrophobic group is in the rz position. (According to Scheduler and Betger [32], the amino add residues in a substrate undergoing cleavage are designated as Pi, P2, P3, etc. in the N-tennmal direction and Pi, Y P3r, etc. in the C-temunal direction from the cleaved bond.) Predominantly Gly-Fhe, Phe-Ser, Tyr-Ile, and "iyr-Val bands are cleaved [33,34]. The specificity of bromelain is different from that of papain and ficin in that it hydrolyzes most effectively derivatives of Lys, Ala, T r, Gly, and Asn [35]. 

The active sites of proteinases not only contain the catalytic site but also specific binding sites on the enzyme surface, which interact noncovalently with individual amino add residues of the polypeptide substrate, The peptide bond hvdrolvzed bv the nroteinase is called the sdssile or Ihe Pl-Pl bond... 

The antibodies are similar in structure to other globulin proteins which are present in serum of vertebrates [9], The antibody molecule consists of two light polypeptide chains and two heavy polypeptide chains [10]. The amino acids are present in all the chains but the number of residues and the sequence will vary in different antibody multiforms [9], Light chains contain approximately 220 amino add residues and heavy chains about 450 residues. The complete sequence of the chains of human IgG myeloma protein has been determined by Edelman [11], The chains are held together in the unique conformational structure of the antibody molecule by a few covalent disulfide bonds between the chains and many electrostatic bonds between the amino groups of one chain and the hydroxyl groups of another chain. The covalent bonds are represented in Formula 1, 2 and 3 [peptide, disulfide and... 

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