Surface amino acids

Creation of covalent bonds between surface amino acids of the enzyme and an insoluble matrix is perhaps the most frequendy exploited method of immobilization. Polar amino acids, which are likely to be present on the protein surface, have struaures that lend themselves to the chemical manipulation necessary for immobilization. e-Amino groups of lysine residues are the most frequendy employed points of linkages, though cysteine (via -SH), tyrosine, histidine, aspartic and glutamic acids, tryptophan, and arginine can also be used. 

It is known that CYP1A2 preferentially binds molecules with a relatively planar moiety, with heterocyclic aromatic amines, xanthines and quinolones. It is also likely that surface amino acid residues are responsible for the recognition of and the selectivity towards specific ligands [11]. 

Terai Y, Morikawa N, Kawakami K ct al. Accelerated evolution of the surface amino acids in the WD-repeat domain encoded by the hagoromo gene in an explosively speciated lineage of east African cichlid fishes. Mol Biol Evol 2002 19(4) 574-78. 

Surface Amino acid Native Exposed surface (A ) Active Change (A) ... 

Several mutants of yeast iso-1-cytochrome c with single-site internal and surface amino acid replacement have been investigated (30) at edge-plane graphite and modified gold electrodes. It is found that midpoint potentials follow the order Lys-13-Ile (+62 5 mV vs. SCE) >... 

Elaboration of LRET mechanism by resolving the parameters that determine specific rates of LRET has stimulated pulse radiolysis studies in proteins. Examples include generation of metastable electron donor and acceptor complexes in (1) native and mutant proteins, (2) proteins with the directed single-site specific mutations, (3) native and mutant multisite redox proteins, (4) proteins with the site specific modification with transition metal complexes covalently attached to a specific surface amino acid residues. 

Experiment 1 the unlabeled proteins are labeled individually to determine the surface amino acids. 

The hydrophobic amino acid residues of globular proteins are generally folded inside the structure or located in a few patches on the surface. As a protein is denatured, the buried amino acids are exposed, yielding more sites for hydrophobic binding. The hydrophobic interaction system thus encounters primarily surface amino acids— far fewer hydrophobic residues than the reversed phase. 

In HIC, the mobile phase should be buffered to provide control of ionization because amino acids which are not ionized are more hydrophobic than those which are charged. The effect of pH on hydrophobicity produces some variation of retention with pH however, it is not directly related to the p/ of the analyte because only surface amino acids interact with the ligands. In a study of the effect of pH on retention by HIC for a series of lysozymes from different bird species, those containing histidine residues in the hydrophobic contact region exhibited deviation for pH values of 6-8, which is near the of histidine... 

Subtilisin (EC 3.4.21.4) an extracellular, single chain, alkaline serine protease from Bacillus subtilis and related species. S. are known from four different species of Bacillus S. Carlsberg (274 amino acid residues, M, 27,277), S. BPN (275 amino acid residues, M, 27,537), S. Novo (identical with S.BPN ) and S. amylosacchariticus (275 amino acid residues, M, 27671). The observed sequence differences between different S. represent conservative substitutions and are limited to the surface amino acids. Like the pancreatic proteinases, S. has catalytic Ser22i, His64 and Asnjj residues, but it is structurally very different from the other serine proteases, e. g. the active center of S. is -Thr-Ser-Met-, whereas that of the pancreatic enzymes is -Asp-Ser-Gly- pancreatic enzymes contain 4- disulfide bridges, whereas S. contains none S. contains 31 % a-helical structure and 3 spatially separated domains, whereas the pancreatic enzymes have 10-20% a-helical structure and a high content of p-structures in both types, the active center is a substrate cleft. S. also have a broader substrate specificity than the pancreatic enzymes. This is a notable example of the convergent evolution of catalytic activity in two structurally completely different classes of proteins. S. is used in the structural elucidation... 

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