Amino-acid residues isoleucine

Fig. 9 Correlation of (A) the second order rate constants (k2 = kcatIKM) and (B) the transition stabilization (pATS) with the hydrophobicity (it) of the substituent of the amino acid residue for the cleavage of /V-acetylamino acid methyl esters by a-chymotrypsin. The open symbols are for the points for two branched residues (valine and isoleucine). Data from Table A6.8.

FIGURE 8.19 Data showing the relative sensitivities to isomerization of /V-methylamino-and amino-acid residues under conditions of saponification, acidolysis by HBr (5.7 M = saturated) in anhydrous acetic acid and aminolysis of the mixed anhydrides by H-Gly-OBzl TosOH/EtgN.94 lie = isoleucine. 

In addition to the amino acids described above, several other amino acid residues are also reactive toward compounds containing heavy atoms. These are the side chains of arginine, asparagine, glutamine, lysine, tryptophan, and tyrosine. Those that are not reactive are alanine, glycine, isoleucine. 

Point mutations that give altered sterol profiles have been generated in A. thaliana and S. cerevisiae LSs. Matsuda and co-workers used a yeast expression system to select for spontaneous mutations in A. thaliana CS that restored sterol-independent growth to an LS-deficient mutant of yeast [67]. In this way they were able to identify a mutation from isoleucine to valine (at Ile481) that allowed synthesis of the sterols lanosterol and parkeol. Further studies have identified a number of other amino acid residues in A. thaliana CS and... 

Biopharmaceuticals based on natural proteins and peptides are often called by the same name as the biologic natural material despite differences in one or more amino-acid residues. For example, insulin, which regulates blood glucose and is used clinically to treat type 1 diabetes and some cases of type 2 diabetes, has several variants that are approved for human use. Insulin contains two polypeptides, A and B chains (Figure 1.2), that are linked together by two disulfide bridges to assume a biologically active conformation. Compared with human insulin, insulin extracted from beef tissue exhibits threonine alanine and isoleucine valine substitutions at posi-... 

FIGURE 17.7 Some important direct interactions between conserved amino acid residues of the active site of influenza A virus sialidase and a-Neu5Ac. Ala, alanine Arg, arginine Asn, asparagine Asp, aspartic acid Glu, glutamic acid His, histidine lie, isoleucine Typ, tryptophan Tyr, tyrosine. 

Figure 14.13. Structure of isoleucine and the expected COSY and TOCSY spectra for this amino acid residue in 90% H2O/10% D20.

Figure 8 Allowed areas of the steric map for various terminally blocked amino acid residues X.45 In area 0, no conformations are allowed. Conformations in areas 1 to 4 are allowed for X = glycine, in areas 2 to 4 for X = alanine, in areas 3 to 4 for higher straight-chain homologs, whereas only area 4 is allowed for X = valine or isoleucine. The circles marked R and L indicate the locations of the standard right-and left-handed a helices on the steric map.

All valence electron MO calculations have been extended to the prediction of amino acid residue conformations. The approach has generally been to consider a model compound, such as an N-acylamino acid amide to simulate the mid-chain residue. Beginning with three independent studies reported in 1969 ( 56—58) a number of amino acid residue conformations have been predicted to date from all valence MO methods. Specific examples of amino acid residues studied, with references in order of appearance in the literature are glycine (56-59), alanine (56, 57, 59), phenylalanine (57), proline (57, 60), hydroxyproline (60), serine (61, 62), isoleucine (61, 88), valine (61,88), threonine (62), leucine (61,88), arginine (N-terminal) (63), arginine (C-terminal) (63), arginine side... 

Initial attempts to achieve an enzyme-catalyzed deprotection of the carboxy group of peptides centred around the use of the endopeptidases chymotrypsin, trypsin,and thermolysin.P l Thermolysin is a protease obtained from Bacillus thermoproteolyticus that hydrolyzes peptide bonds on the annino side of the hydrophobic amino acid residues (e.g., leucine, isoleucine, valine, phenylalanine). It cleaved the supporting tripeptide ester H-Leu-Gly-Gly-OEt from a protected undecapeptide (pH 7, rt). The octapeptide, thus obtained, is composed exclusively of hydrophilic annino acids. Due to the broad substrate specificity of thermolysin and the resulting possibility of unspecific peptide hydrolysis, this method is of limited application. 

Two main classes of ions are formed by CID, those that contain the C terminus plus one or more additional residues (ions of types x , y , and z ) and those that contain the N-terminus and one or more additional residues (ions of types a , b , and c ). Ions of types y and b are formed by the rupture of amide bonds, and the mass differences between these fragments are limited to the masses of the naturally occurring 19 different amino acid residues (Table 15.9). Isoleucine and leucine,... 

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