Valine requirements

Data was subjected to ANOVA with diet as fixed effect, and litter as a random effect. Valine requirement was determined by a curvilinear-plateau model (Robbins et al, 2006). 

Valine requirement of weaned piglets fed low-protein diet... 

Many kinds of amino acids (eg, L-lysine, L-omithine, t-phenylalanine, L-threonine, L-tyrosine, L-valine) are accumulated by auxotrophic mutant strains (which are altered to require some growth factors such as vitamins and amino acids) (Table 6, Primary mutation) (22). In these mutants, the formation of regulatory effector(s) on the amino acid biosynthesis is genetically blocked and the concentration of the effector(s) is kept low enough to release the regulation and iaduce the overproduction of the corresponding amino acid and its accumulation outside the cells (22). 

Adenosylcobalamin (coenzyme B 2) is required in a number of rearrangement reactions that occurring in humans is the methylmalonyl-Co A mutase-mediated conversion of (R)-methylmalonyl-Co A (6) to succinjl-CoA (7) (eq. 1). The mechanism of this reaction is poorly understood, although probably free radical in nature (29). The reaction is involved in the cataboHsm of valine and isoleucine. In bacterial systems, adenosylcobalamin drives many 1,2-migrations of the type exemplified by equation 1 (30). 

The elegant genetic studies by the group of Charles Yanofsky at Stanford University, conducted before the crystal structure was known, confirm this mechanism. The side chain of Ala 77, which is in the loop region of the helix-turn-helix motif, faces the cavity where tryptophan binds. When this side chain is replaced by the bulkier side chain of Val, the mutant repressor does not require tryptophan to be able to bind specifically to the operator DNA. The presence of a bulkier valine side chain at position 77 maintains the heads in an active conformation even in the absence of bound tryptophan. The crystal structure of this mutant repressor, in the absence of tryptophan, is basically the same as that of the wild-type repressor with tryptophan. This is an excellent example of how ligand-induced conformational changes can be mimicked by amino acid substitutions in the protein. 

The classical cadherins are translated as precursor because they are N-terminally cleaved to reveal the mature proteins. This processing is required to activate the cell adhesion function of cadherins. Cadherins interact in trans (i.e., from opposite cells) via the most N-terminal cadherin rqDeats. A short amino acid sequence within this repeat, histidine-alanine-valine (HAV), has been implicated in mediating cell-cell contacts as HAV peptides can disrupt cadherin-dependent cell adhesion. Besides the trans-interactions of cadherins, the extracellular domains are also capable of forming cis-dimers through lateral amino acid contacts between cadherin molecules on one cell. This dimerization again mainly involves the first cadherin repeat. A zipper model based on the pattern of alternating cis- and trans-dimers [1] for the adhesive interactions has been proposed. 

Not all proteins are nutritionally equivalent. Mote of some than of others is needed to maintain nittogen balance because different proteins contain different amounts of the various amino acids. The body s requirement is for specific amino acids in the correct proportions to replace the body proteins. The amino acids can be divided into two groups essential and nonessential. There are nine essential or indispensable amino acids, which cannot be synthesized in the body histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. If one of these is lacking or inadequate, then—regardless of the total intake of protein—it will not be possible to maintain nitrogen balance since there will not be enough of that amino acid for protein synthesis. 

Zincate reagents can add to imines with or without Lewis acid catalysis. Alkylimines require BF3 but imines of pyridine-2-carboxaldehyde react directly. If the imines are derived from chiral amines, diastereoselectivity is observed. Both a-phenylethyl amine and ethyl valinate have been tried. Higher enantioselectivity was observed with mixed magnesium reagents.175... 

In mammals and in the majority of bacteria, cobalamin regulates DNA synthesis indirectly through its effect on a step in folate metabolism, catalyzing the synthesis of methionine from homocysteine and 5-methyltetrahydrofolate via two methyl transfer reactions. This cytoplasmic reaction is catalyzed by methionine synthase (5-methyltetrahydrofolate-homocysteine methyl-transferase), which requires methyl cobalamin (MeCbl) (253), one of the two known coenzyme forms of the complex, as its cofactor. 5 -Deoxyadenosyl cobalamin (AdoCbl) (254), the other coenzyme form of cobalamin, occurs within mitochondria. This compound is a cofactor for the enzyme methylmalonyl-CoA mutase, which is responsible for the conversion of T-methylmalonyl CoA to succinyl CoA. This reaction is involved in the metabolism of odd chain fatty acids via propionic acid, as well as amino acids isoleucine, methionine, threonine, and valine. 

S)-Isopropylmorpholine-2,5-dione, six-membered depsipeptide, was polymerized by lipase PC and PPL catalysts [112]. High temperature (100°C or 130°C) was required for the polymerization, yielding biodegradable poly(de-psipeptide). During the polymerization, the racemization of the valine residue took place. Demonstrated was PPL-catalyzed ring-opening polymerization of ethylene isopropyl phosphate, five-membered cyclic phosphate [113]. 

Many organic acidurias originate in the breakdown of the three branched-chain amino acids, leucine, isoleucine and valine (Fig. 40-1). Metabolism of the organic acids requires the presence of specific enzymes, congenital... 

The main disadvantages of Evans auxiliaries 22 and 23 are that they are expensive to purchase and inconvenient to prepare, as the preparation involves the reduction of (5 )-valine 24 to water-soluble (b )-valinol, which cannot be readily extracted to the organic phase. The isolation of this water-soluble vali-nol is difficult and requires a high vacuum distillation, which is not always practical, especially on an industrial scale. Therefore, an efficient synthesis of Evans chiral auxiliary 25 has been developed, as depicted in Scheme 2-1930 ... 

The second filtrate from the reciystallization together with the filtrate from the original concentration is evaporated to dryness and extracted with 500 cc. of glacial acetic acid on a steam cone. The inorganic salts are filtered and the acetic acid is removed by distillation under reduced pressure. One liter of water is added, and it, too, is removed by distillation under reduced pressure. This operation is repeated. These three distillations require one day. The residue is dissolved in the minimum amount of hot water (about 300 cc.). The solution is then treated with Norite as before and filtered hot, and an equal volume of 95 per cent alcohol is added. The yield on cooling overnight in the icebox is 34 g. An additional 8 g. can be obtained from the mother liquor by concentration and addition of alcohol as was done with the original mother liquor. T e total yield of valine is 300-311 g. (47-48 per cent of the theoretical amount),... 

Humans have a limited capacity to synthesize amino acids de novo, but extensive interconversions can occur. Those amino acids which cannot be formed within the body and must be supplied by the diet are called essential . Members of this group, which includes the branched chain amino acids leucine and valine, and also methionine and phenylalanine, are all dietary requirements. Such essential amino acids may be chemically converted, mainly in the liver, into the non-essential amino acids. The term non-essential does not equate with not biochemically important but simply means they are not strict dietary components. 

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