Valine, characteristics

The DQFCOSY spectrum of RpII in D O is shown in Figure 2. Each cross peak in this spectrum identifies a pair of coupled spins of the amino acid side chains. Since couplings are not propagated efficiently across amide bonds, all groups of coupled spins occur within individual amino acids. The chemical structure of an amino acid side chain is reflected in the characteristic coupling network and chemical shifts (13). Valine spin system (CH-CH-(CH3)2) explicitly shown in Figure 2 as an example. 

Especially in the case of high-molecular-weight surface-active substances (such as proteins), the period of change may be sufficiently prolonged to allow easy observation. This arises because proteins are surface active. All proteins behave as surface-active substances because of the presence of hydrophilic-lipophilic properties imparted from the different polar, such as glutamine and lysine, and apolar, such as alanine, valine, phenylalanine, isovaline, amino acids. Proteins have been extensively investigated as regards their polar-apolar characteristics as determined from surface activity. 

T There is a relatively rare genetic disease in which the three branched-chain a-lceto acids (as well as their precursor amino acids, especially leucine) accumulate in the blood and spill over into the urine. This condition, called maple syrup urine disease because of the characteristic odor imparted to the urine by the a-lceto acids, results from a defective branched-chain a-lceto acid dehydrogenase complex. Untreated, the disease results in abnormal development of the brain, mental retardation, and death in early infancy. Treatment entails rigid control of the diet, limiting the intake of valine, isoleucine, and leucine to the minimum required to permit normal growth. ... 

Maple syrup urine disease (MSUD) is a recessive disorder in which there is a partial or complete deficiency in branched-chain o-ketoacid dehydrogenase, an enzyme that decarboxylates leucine, isoleucine, and valine (see Figure 20.10). These amino acids and their corre sponding a-keto acids accumulate in the blood, causing a toxic effect that interferes with brain functions. The disease is characterized by feeding problems, vomiting, dehydration, severe metabolic acidosis, and a characteristic maple syrup odor to the urine. If untreated, the disease leads to mental retardation, physical disabilities, and death. 

The properties of polypeptides and proteins are determined to a large extent by the chemistry of the side chain groups, which may be summarized briefly as follows. Glycine in a peptide permits a maximum of conformational mobility. The nine relatively nonpolar amino acids-alanine, valine, leucine, isoleucine, proline, methionine, phenylalanine, tyrosine, and tryptophan-serve as building blocks of characteristic shape. Tyrosine and tryptophan also participate in hydrogen bonding and in aromatic aromatic interactions within proteins. 

Valencia oil. see Citrus Orange Valine, hydrolysis, effect on, 134 Vapor pressure, 4. see Water activity Vapor pressure manometer (VPM), 61 -66 Vegetable oils characteristics of, 525 refined, tocopherol/tocotrienol... 

The characteristic absorptions in the i.r. spectra of lactones and amino acids are discussed on pp. 302 and 308 respectively the spectra of (DL)-valine and l-tryptophan are given in Figs 3.36 and 3.37. Further descriptive spectral interpretations for a range of substituted carboxylic acids and their derivatives are given in appropriate preparative sections. 

Free amino acids are further catabolized into several volatile flavor compounds. However, the pathways involved are not fully known. A detailed summary of the various studies on the role of the catabolism of amino acids in cheese flavor development was published by Curtin and McSweeney (2004). Two major pathways have been suggested (1) aminotransferase or lyase activity and (2) deamination or decarboxylation. Aminotransferase activity results in the formation of a-ketoacids and glutamic acid. The a-ketoacids are further degraded to flavor compounds such as hydroxy acids, aldehydes, and carboxylic acids. a-Ketoacids from methionine, branched-chain amino acids (leucine, isoleucine, and valine), or aromatic amino acids (phenylalanine, tyrosine, and tryptophan) serve as the precursors to volatile flavor compounds (Yvon and Rijnen, 2001). Volatile sulfur compounds are primarily formed from methionine. Methanethiol, which at low concentrations, contributes to the characteristic flavor of Cheddar cheese, is formed from the catabolism of methionine (Curtin and McSweeney, 2004 Weimer et al., 1999). Furthermore, bacterial lyases also metabolize methionine to a-ketobutyrate, methanethiol, and ammonia (Tanaka et al., 1985). On catabolism by aminotransferase, aromatic amino acids yield volatile flavor compounds such as benzalde-hyde, phenylacetate, phenylethanol, phenyllactate, etc. Deamination reactions also result in a-ketoacids and ammonia, which add to the flavor of... 

Touraille, C.J., Kopp, ]., Valin, C. and Ricard, F.H. (1981) Chicken meat quality. 1. Influence of age and growth rate on physico-chemical and sensory characteristics of the meat. Archivfiir Gefliigelkunde 45,69-76. 

Is and PBPRP1 may then represent an OBP-1 type of protein defined by key residues that may underlie specific functions. The ABPX/PBPRP-specific amino acid residues arginine at position 16, lysine at position 47, proline at position 76, threonine at position 92 are replaced respectively by leucine, glycine, lysine and lysine residues that are conserved in the different types of binding protein from B. mori (Krieger et al., 1993 Picimbon, 2001). These replacements may be relevant to support the function of ABPX. Based on the crystal structure of the bombykol-PBP complex, the tryptophane at position 101 and the valine 105 have been shown to contact the molecule of Bombykol (Sandler et al., 2000). These are replaced by two threonine residues characteristic of OBP-1. Therefore, the threonine residues characteristic of OBP Is may be of crucial importance for the binding specificities of these proteins. 

The shapes of the growth curves after the depletion point show characteristic and reproducible differences from one limiting amino acid to another. The most striking example of these differences is illustrated by Figure 3, in which the depletion points of a valine-limited... 

In this chapter the sorption of two organic substances, EDTA and valine amino acid, are discussed. They were selected for two reasons as seen in Figure 2.8, EDTA can be sorbed on the edge sites of montmorillonite. The other reason is the presence of characteristic functional groups in both molecules. The carboxylic and amine groups are very important in organic syntheses and also in humic substances. 

In alkaline medium, the aluminol sites are deprotonated (Alt) ). Also, the characteristic species of valine is negatively charged and cannot be adsorbed by negative A10 sites. 

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