Valine relative hydrophobicity

As noted by the original authors (Dorovska et al., 1972), and cited by Fersht (1985), there is an excellent linear correlation between log/ccat/KM and the Hansch hydrophobicity parameters (v) of the side chains (Fig. 9, A), except for the two branched side chains (valine and isoleucine residues). However, since the ku values for the esters do vary somewhat (Table A6.8), the values of pKrs do not correlate as strongly with ir (Fig. 9, B). Moreover, the plot shows distinct curvature which probably indicates the onset of a saturation effect due to the physical limits of the Sj binding pocket, adjacent to the enzyme s active site. Still, the points for valine and isoleucine deviate below the others, suggesting that the pocket has a relatively narrow opening. 

Irreversible insolubilization of proteins may occur mainly through formation of both intermolecular disulfide and hydrophobic bonds. The product can be quite different depending on the relative contribution of these two types of bonds. The hydrophobic bonds are formed among the hydrophobic amino acid side chains contributed by valine, leucine, isoleucine, phenylalanine, etc. 

COX-1 and COX-2 are of similar molecular mass (approximately 70 and 72 kDa respectively), with 65% amino acid sequence homology and near-identical catalytic sites. The most significant difference between the isoenzymes, which allows for selective inhibition, is the substitution of isoleucine at position 523 in COX-1 with valine in COX-2. The relatively smaller Val523 residue in COX-2 allows access to a hydrophobic side-pocket in the enzyme (which Ile523 sterically hinders). Drugs, such as the coxibs, bind to this alternative site and are considered to be selective inhibitors of COX-2. 

The term lyophobic interactions is intended to generalize the expres sion hydrophobic interactions to other solvents than water. Hydro-phobic interactions have been prominently implicated in determining the native configuration of proteins in aqueous solution. These interactions are actually not of a single relatively well-defined character, as are electrostatic or hydrogen bond interactions, but are rather a set of interactions responsible for the immiscibility of nonpolar substances and water. Proteins contain a substantial proportion of amino acids such as phenylalanine, valine, leucine, etc., with nonpolar side-chain residues. These nonpolar groups should tend, therefore, other factors permitting, to cluster on the... 

Effects of amino acids The effects of 18 kinds of amino acids on crystal appearance are summarized in table 4. Among these amino acids tested, only leucine and tryptophan affected the change in crystal form from pillars to thin plates at concentrations relative to Lmore than 3%. These two amino acids are hydrophobic, so they might interact with the Lrphenylalanine skeleton in the crystal structure of di-L-phenylalanine sulfate monohydrate and are supposed to suppress growth in the a-axis direction. Isoleucine, valine and tyrosine which are analogous... 

Effect of Different Pentamer Sequence Arrangements of the Same 30-mer Composition. Chemically synthesized polytricosapeptides, poly (30-mers), were prepared with compositions of 1 aspartic acid residue (Asp, D) and 5 more-hydrophobic phenylalanine (Phe, F) residues replacing valine (Val, V) residues per repeat of 30 residues, but with different relative locations of D and F residues. These compositions are written ... 

The thermodynamic stability, the aggregation state, and the relative orientation of the helical strands in such peptides were shown to depend largely on the identity of the amino acid residues at positions a, d, e, and g. The use of leucine and valine at the hydrophobic core (positions a and glutamic acid and lysine at the e and g positions were shown to control equilibrium between dimeric and trimeric coiled-coil aggregation states." Peptide sequences that allow interconversion between dimeric and trimeric parallel coiled coils were found as productive templates to enhance substrate selectivity, catalytic efficiency, and turnover and were commonly used in peptide-replicating systems. 

For assembly of novel three-dimensional (3D) structures, block copolypeptides are required that have structural domains (i.e., amino acid sequences) whose size and composition can be precisely adjusted. Such materials have proven elusive using conventional techniques. Strong base-initiated NCA polymerizations are very fast. These polymerizations are poorly understood and well-defined block copolymers cannot be prepared. Primary amine-initiated NCA polymerizations are also not free of side reactions. Even after fractionation of the crude preparations, the resulting polypeptides are relatively ill-defined, which may complicate unequivocal evaluation of their properties and potential applications. Nevertheless, there are many reports on the preparation of block copolypeptides using conventional primary amine initiators. Examples include many hydrophilic-hydrophobic and hydrophilic-hydrophobic-hydrophilic di- and triblock copolypeptides (where hydrophilic residues were glutamate and lysine, and hydrophobic residues were leucine, valine, isoleucine, phenylalanine, and alanine" ) prepared to study... 

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