Isoleucine solubility

Bacitracin is produced and marketed as a mixture of at least nine water-soluble peptides. The principal (60 —80%) component is bacitracin A [22601-59-8], C33H2Q3N2y02gS. The most probable stmcture of bacitracin A is shown in Figure 1 (67,73). Bacitracin B [1402-99-9] is similar to bacitracin A except that one of the isoleucines of bacitracin A is replaced by a valine. Bacitracin F [22601-63-4], is a relatively inactive degradation... 

BicoZamycin. Bico2amycin (bicyclomycin) [38129-37-2] C22H2gN20y, shown in Figure 6, is a colorless, water-soluble diketopipera2ine or cycHc dipeptide derived from leucine and isoleucine. It was simultaneously isolated in 1972 in Japan from cultures of two different strains (166). 

Most of the naturally-occurring pyrazine hydroxamic acids appear to be derived from valine, leucine and isoleucine, and biosynthetic studies by MacDonald and coworkers (61JBC(236)512, 62JBC(237)1977, 65JBC(240)1692) indicate that these amino acids are incorporated. However, it would seem that the logical intermediates, viz. the 2,5-dioxopiperazines such as (111) and (112), are not always incorporated. This does not rule out their intermediacy, as there may be problems such as low solubility or membrane permeability which prevent their efficient incorporation. An exception to these results was reported for pulcherrimic acid (113) (65BJ(96)533), which has been shown to be derived from cyclo-L-leu-L-leu which serves as an efficient precursor. 

One of the sex pheromone components of the housefly, Musca domestica, is Z9-21 H that is found on the cuticular surface of the fly. This compound is formed by the elongation of Z9-18 CoA using malonyl-CoA and NADPH to Z15-24 CoA which is decarboxylated to form Z9-21 Hc (Fig. 3) [78-80]. Other pheromone components include an epoxide and ketone that are produced from Z9-21 Hc by a cytochrome P450 [81,82] and methyl-branched alkanes that are produced by the substitution of methylmalonyl-CoA in place of malonyl-CoA at specific points during chain elongation [83,84]. A novel microsomal fatty acid synthase is involved in production of methyl-branched alkanes in most insects [85-87]. This fatty acid synthase is different from the ubiquitous soluble fatty acid synthase that produces saturated straight chain fatty acids in that it is found in the microsomes and prefers methylmalonyl-CoA. The amino acids valine and isoleucine can provide the carbon skeletons for methylmalonyl-CoA as well as propionate [83]. 

Morris A.E., Remmele R.L. Jr., Klinke R., Macduff B.M., Fanslow W.C., and Armitage R.J. (1999), Incorporation of an isoleucine zipper motif enhances the biological activity of soluble CD40L (CD154), J. Biol. Chem. 27, 418—423. 

For crystallization by acid addition, the effects of acid addition rate, agitation, and initial solution composition were examined. The experiments had constant initial and final temperatures, although there were some variations in temperature during a run because of the heat of crystallization of L-isoleucine hydrochloride (L-Ile HCl H20) and heat of solution of acid. The acid used was in the form of 37% HCl. The initial conditions of the batch corresponded to an HCl concentration giving the maximum solubility of L-Ile (1). A schematic of the batch crystallizer is shown in Figure 3. 

Leucine.—The greater part of the leucine is contained in the ester fractions, which boil between 70° and 90° C. It generally occurs in considerable amounts in the protein, and is obtained by crystallisation from water, in which it is less soluble than the other amino acids which may be present. It is seldom present in its pure, optically active form, as this is easily racemised, and the various crops of crystals most probably also contain isoleucine. It is more easily isolated by completely racemis-ing the mixture of amino acids contained in this fraction by heating in an autoclave with baryta to 160-180° C., and then, after removal of the baryta, separating it by crystallisation. The difficulty of separating it from the other amino acids, especially valine and isoleucine, makes an exact quantitative estimation almost impossible. The values which have been found are therefore minimal ones, and they will also include in many cases the yield of isoleucine. 

Concentrated hydrochloric acid is diluted by its own volume with water. Hydrochloric acid (2.4 L, 5 N) is employed for the less soluble (S)-araino acids valine, leucine and isoleucine. 

The synthesis and characterization of water-soluble, random copolymers containing L-isoleucine with AAO-hydroxypropyD-L-glutamine, and the thermally induced helix-coil transitions of these copolymers in water, are described. The incorporation of L-isoleucine is found to increase the helix content of the copolymers in water at all temperatures considered. The Zimm-Bragg parameters helix-coil transition in poly(L-isoleucine) in water are deduced from an analysis of the melting curves. Values of the Zimm-Bragg parameters s for poly(L-lsoleucine) in water are computed with the Lifson (o = 5.1 x 10 3) / Aiiegra (o = 5.5 x 10 3) approximation s = 1.20/1.25 (273 K), 1.11/1.14 (293 K), 1.07/1.08 (313 K), and 1.01/1.01 (333 K). 

DL-Isoleucine occurs as a white, crystalline powder. It is soluble in water, and practically insoluble in alcohol and in ether. It melts with decomposition at about 292°. The pH of a 1 100 aqueous solution is between 5.5 and 7.0. It is optically inactive. 

However, in the cases examined so far, the molar solubility in DMF has not increased significantly. The 1-adamantyloxycarbonyl (1-Adoc) group could potentially improve the solubility of amino acids and peptides protected by 1-Adoc in organic solvents due to its strong hydrophobicity.P Lys(l-Adoc) was successfully employed in the synthesis of peptide histidine isoleucine (PHI) (Scheme 9)P9 and in the synthesis of a peptide fragment of a lysozyme.P l... 

Besides solid material surfaces, functional water-soluble polymers have also been created to promote cell-cell adhesion in aqueous media. For example, cell adhesion peptides of RGD or tyrosine-isoleucine-glycine-serine-arginine (YIGSR) have been attached to the ends of biofunctional PEG and shown to induce neural cell aggregation in culture media. ° ... 

These branched-chain aliphatic amino acids contain bulky nonpolar R-groups and participate in hydrophobic interactions. All three are essential amino acids. A defect in their catabolism leads to maple syrup urine disease (Chapter 17). Isoleucine has asymmetrical centers at both the a- and 8-carbons and four stereoisomers, only one of which occurs in protein. The bulky side chains tend to associate in the interior of water-soluble globular proteins. Thus, the hydrophobic amino acid residues stabilize the three-dimensional structure of the polymer. 

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