Glycine relative hydrophobicity

Transport of amino acids across a chloroform liquid membrane with these carriers also revealed a high specificity (Scheme 2). For efficient transport, an aromatic side chain must be present and the distance between the aryl and ammonium functions is optimal in the P-aryl systems. Neither oe-phenyl-glycine 42 nor y-phenyl-butyrine 43 are transported to significant extents 25a>. These results are shown in Table 2. The selectivity with 13 contrasts sharply for that observed with typical detergents wherein side chain hydrophobicity determines the relative transport rates. 

The results of kinetic and X-ray crystallographic experiments on mutant carbonic anhydrases II, in which side-chain alterations have been made at the residue comprising the base of the hydrophobic pocket (Val-143), illuminate the role of this pocket in enzyme-substrate association. Site-specific mutants in which smaller hydrophobic amino acids such as glycine, or slightly larger hydrophobic residues such as leucine or isoleucine, are substituted for Val-143 do not exhibit an appreciable change in CO2 hydrase activity relative to the wild-type enzyme however, a substitution to the bulky aromatic side chain of phenylalanine diminishes activity by a factor of about 10 , and a substitution to tyrosine results in a protein which displays activity diminished by a factor of about 10 (Fierke et o/., 1991). 

A more extensive study of mobilities of 3H- and 14C-labeled amino acids again found that amino acids labeled with 14C at Cl or C2 are retained on the column, relative to the unlabeled forms.135 Lysine is an exception. Tritiation at C3 also increases the retention time, but tritiation at C2 of glycine or at C4, C5, or C6 of lysine decreases it, and large decreases are seen with methionine tritium-labeled in the methyl and with tyrosine tritium-labeled at C3, 5. The 14C IEs can be attributed to a decrease of acidity, but the IEs of distant 3H may be due to hydrophobic interactions with the resin. A remarkable result is that intramolecular isotopic isomers (isotopomers) can be distinguished on the basis of their chromatographic mobilities. 

The f values of the single amino acids given in Table I were determined by Tanford (2) from solubility data and they represent a measure of the hydrophobicity of an amino acid residue. Please note, that the values are relative to the methyl groups of glycine which is taken to be O. In Table II the taste of some "isomericn-dipeptides is described. All the dipeptides are composed of the natural 1-amino acids, as are all the examples, that will follow later. It is interesting to note, that the position of the amino acid has no influence on bitterness ( ). 

A well-studied system is alanine dipeptide (AcAlaNHMe). The relative stability of different conformational states in vacuum - and in water were obtained from PMF calculations, °> and again different models and simulation parameters were applied. In a recent study Marrone, Gilson, and McCammon calculated the PMF of alanine dipeptide by using the Pois-son-Boltzmann method with a hydrophobic term and by using explicit water and found comparable results. Fraternali and van Gunsteren studied PMFs of glycine dipeptide in water for two reaction coordinates. Tobias and Brooks used their own technique to calculate the PMF of the central torsional angle... 

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