A valine

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... 

A valine-based chiral oxazaborolidinone 80 (generated in situ from Ts-L-Val and BH3-THF) was used by Kiyooka and co-workers [37] to catalyse the reaction be-... 

A valine-derived oxazaborolidine derivative has been found to be subject to activation by Lewis acids, with SnCl4 being particularly effective.98 This catalyst combination also has reduced sensitivity to water and other Lewis bases. 

Sickle cell disease is caused by a mutation that results in the substitution of a valine residue for a glutamate residue in the sixth position of the hemoglobin P-chain. This results from the substitution of a T for an A in the glutamate codon. When (1) DNA from a patient... 

Besides the synthetic inhibitors, a variety of natural compounds is known to inhibit the CP. One of these natural inhibitors, lactacystin, was discovered by its ability to induce neurite outgrowth in a murine neuroblastoma cell line. Incubation of cells in the presence of radioactive lactacystin leads to the labelling of the yS5 subunit (Fenteany et al. 1995) and to irreversible inhibition of the CP. As shown by X-ray analysis, the inhibitor is covalently attached to subunit fS5 by an ester bond with the N-terminal ThrlO (Groll et al. 1997) (see Figure 10.7A). The subunit selectivity of lactacystin can be attributed to its dimethyl group, which mimics a valine or a leucine side chain and closely interacts with Met45 in the hydrophobic SI pocket of subunit j85. 

Now we can ask what is likely to happen to the three-dimensional structure of a protein if we make a conservative replacement of one amino acid for another in the primary structnre. A conservative replacement involves, for example, substitution of one nonpolar amino acid for another, or replacement of one charged amino acid for another. Intnitively, one would expect that conservative replacements would have rather little effect on three-dimensional protein structure. If an isoleucine is replaced by a valine or leucine, the structnral modification is modest. The side chains of all of these amino acids are hydrophobic and will be content to sit in the molecnlar interior. This expectation is borne out in practice. We have noted earlier that there are many different molecnles of cytochrome c in nature, all of which serve the same basic function and all of which have similar three-dimensional structnres. We have also noted the species specificity of insulins among mammalian species. Here too we find a number of conservative changes in the primary structure of the hormone. Although there are exceptions, as a general rule conservative changes in the primary structnre of proteins are consistent with maintenance of the three-dimensional structures of proteins and the associated biological functions. 

Hashimoto and co-workers, on the other hand, studied the intramolecular reaction between cyclic carbonyl yield and dimethyl acetylenedicarboxylate (DMAD) (Equation (14)). With dirhodium(ii) tetrakis[A-benzene-fused phthaloyl-(A)-valinate] [Rh2(WBPTV)4] 104, high enantioselectivity (68-92% ee) was achieved over a range of diazo substrates.The high level of enantiocontrol provided conclusive evidence that chiral Rh(ii) catalyst is associated with the ylide in the cycloaddition step. 

For many years patients with diabetes were treated with insulins that had been isolated from the pancreases of pigs and cows. The primary sequences of these insulins are closely related to the sequence of human insulin. There is only a single difference between the sequences of human and porcine insulins human insulin has a threonine at position B30, and porcine insulin has an alanine. Bovine insulin differs from human insulin at three positions. There is an alanine at the B30 position, an alanine at A8, and a valine at A10. These conservative changes in primary sequence have no apparent effect on biologic activity, although there are slight differences in solubility (7). 

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