Branch-chained amino acids

Atrial natriuretic peptide Adenosine triphosphate Concentration in arterial blood minus that in venous blood Branched chain amino acid Branched chain kcto acid Body mass index Basai metabolic rate Biological value Cyclic AMF Cholecystokinin Cholcsteryl ester Complementary DNA Coenzyme A Cocn yme A... 

Uptake and Intracellular Consumption of Amino Acids Branched-chain Amino Acids Interorgan Relationship Summary... 

Traditionally fermented dairy products have been used as beverages, meal components, and ingredients for many new products [60], The formation of flavor in fermented dairy products is a result of reactions of milk components lactose, fat, and casein. Particularly, the enzymatic degradation of proteins leads to the formation of key-flavor components that contribute to the sensory perception of the products [55], Methyl ketones are responsible for the fruity, musty, and blue cheese flavors of cheese and other dairy products. Aromatic amino acids, branched-chain amino acids, and methionine are the most relevant substrates for cheese flavor development [55]. Volatile sulfur compounds derived from methionine, such as methanethiol, dimethylsulflde, and dimethyltrisul-fide, are regarded as essential components in many cheese varieties [61], Conversion of tryptophan or phenylalanine can also lead to benzaldehyde formation. This compound, which is found in various hard- and soft-type cheeses, contributes positively to the overall flavor [57,62]. The conversion of caseins is undoubtedly the most important biochemical pathway for flavor formation in several cheese types [62,63]. A good balance between proteolysis and peptidolysis prevents the formation of bitterness in cheese [64,65],... 

Disorders affecting all three branched-chain amino acids Branched-chain keto aciduria (maple syrup urine disease)... 

Useful for carboxylic acids, branched-chain fatty acids, oxalic acid, amino acids, lipids HCI serves as a catalytic agent... 

Some catabolic reactions of amino acid carbon chains are easy transformations to and from TCA cycle intermediates—for example, the transamination of alanine to pyruvate. Reactions involving 1-carbon units, branched-chain, and aromatic amino acids are more complicated. This chapter starts with 1-carbon metabolism and then considers the catabolic and biosynthetic reactions of a few of the longer side chains. Amino acid metabolic pathways can present a bewildering amount of material to memorize. Perhaps fortunately, most of the more complicated pathways lie beyond the scope of an introductory course or a review such as this. Instead of a detailed listing of pathways, this chapter concentrates on general principles of amino acid metabolism, especially those that occur in more than one pathway. 

Vitamin B12 is essential for the methylmalonyl-CoAmutase reaction. Methylmalonyl-CoA mutase is required during the degradation of odd-chain fatty acids and of branched-chain amino acids. Odd-chained fatty acids lead to propionyl-CoA as the last step of P-oxida-tion. Methylmalonyl-CoA can be derived from propionyl-CoA by a carboxylase reaction similar to that of fatty acid biosynthesis. The cofactor for this carboxylation reaction is biotin, just as for acetyl-CoA carboxylase. The reaction of methylmalonyl-CoA mutase uses a free radical intermediate to insert the methyl group into the dicar-boxylic acid chain. The product is succinyl-CoA, a Krebs cycle intermediate. The catabolisms of branched-chain lipids and of the branched-chain amino acids also require the methylmalonyl-CoA mutase, because these pathways also generate propionyl-CoA. 

The side chain dihedral angle Xi is important for high-resolution definition of protein structures as it determines the angle at which each amino acid side chain branches out from the protein backbone. Moreover, in combination with certain types of NOEs, it can allow stereospecific assignment of prochiral /3-methylene protons, which improves the precision of NMR structures by obviating the need to include pseudoatom distance corrections.140-142... 

Isomerases that are dependent on coenzyme B12 constitute the largest subfamily of Bi2 enzymes and are components of a number of fermentative pathways in microbes [10, 11]. A single member of this group of enzymes, methylmalonyl-CoA mutase, is found in both bacteria and in mammals where it is a mitochondrial enzyme involved in the catabolism of odd-chain fatty acids, branched chain amino... 

Two amino acid side chains—serine and threonine—contain alcohol groups. Serine is an HO-substituted alanine and threonine has a branched ethanol substituent. There are also two sulfur-containing amino acids Cysteine is an HS-substituted alanine and methionine has a 2-methylthioethyl substituent. 

The SAR study on phosphoramidate prodrugs of PSI-6206 was focused on the aryloxy-phosphoramidate side chain. Compared to the common aryloxy-phosphoramidate prodrugs, modifications at amino acid ester, aryl phosphate ester, and amino acid side chain were conducted on PSI-6206 phosphoramidate. An examination of these modifications for 29 compounds found that a small simple alkyl and branched alkyl at the amino acid ester, phenyl and halogenated aryl at the phosphate ester, and a-methyl at the amino acid side chain produced better antiviral activity and the least cytotoxicity. The groups for the amino acid ester part (R ) were chosen from methyl, ethyl, isopropyl, and cyclohexyl the groups for the aryl phosphate ester (R ) were selected from phenyl and para-halogenated phenyl and the substituent for the amino acid side chain was fixed with a-methyl (r-alanine). These combinations of modifications resulted in 16 compounds (12-27, Table 1) for further evaluation. 

In humans, methylmalonyl-CoA mutase is required for the metabolism of proprionate, derived from branched-chain amino acids, odd-chain fatty acids and cholesterol, into succinyl-CoA (Banerjee 1997 Pett et at. 2002). Methylmalonyl-CoA mutase requires AdoCbl as a cofactor. The mechanism involves the homolytic cleavage of the Co-C bond, forming cob(II)alamin and a 5 -deoxyadenosyl radical (Pett et at. 2002). The homolytic cleavage of the Co-C bond is increased 10 -fold in the presence of the enzyme. The 5 -deox-yadenosyl radical first abstracts a hydrogen atom from the substrate methyl-malonyl-CoA, which donates after a rearrangement reaction back to form succinyl-CoA (Pett et at. 2002). In humans, deficiency in methylmalonyl-CoA mutase causes an inherited metabolic disorder and is one of causes of methylmalonylacidemia. According to the severity of methylmalonyl-CoA mutase reduced activity, the deficiency is characterized as muf (detectable... 

Herbicides also inhibit 5- (9/-pymvylshikiniate synthase, a susceptible en2yme in the pathway to the aromatic amino acids, phenylalanine, tyrosine and tryptophan, and to the phenylpropanes. Acetolactate synthase, or acetohydroxy acid synthase, a key en2yme in the synthesis of the branched-chain amino acids isoleucine and valine, is also sensitive to some herbicides. Glyphosate (26), the sulfonylureas (136), and the imida2oles (137) all inhibit specific en2ymes in amino acid synthesis pathways. 

In the case of hyperphenylalaninaemia, which occurs ia phenylketonuria because of a congenital absence of phenylalanine hydroxylase, the observed phenylalanine inhibition of proteia synthesis may result from competition between T.-phenylalanine and L-methionine for methionyl-/RNA. Patients sufferiag from maple symp urine disease, an inborn lack of branched chain oxo acid decarboxylase, are mentally retarded unless the condition is treated early enough. It is possible that the high level of branched-chain amino acids inhibits uptake of L-tryptophan and L-tyrosiae iato the brain. Brain iajury of mice within ten days after thek bkth was reported as a result of hypodermic kijections of monosodium glutamate (MSG) (0.5—4 g/kg). However, the FDA concluded that MSG is a safe kigredient, because mice are bom with underdeveloped brains regardless of MSG kijections (106). 

In Parenteral and Enteral Nutrition. Amino acid transfusion has been widely used since early times to maintain basic nitrogen metaboHsm when proteinaceous food caimot be eaten. It was very difficult to prepare a pyrogen-free transfusion from protein hydrolysates. Since the advances in L-amino acid production, the crystalline L-amino acids have been used and the problem of pyrogen in transfusion has been solved. The formulation of amino acid transfusion has been extensively investigated, and a solution or mixture in which the ratio between essential and nonessential amino acid is 1 1, has been widespread clinically. Special amino acid mixtures (eg, branched chain amino acids-enriched solution) have been developed for the treatment of several diseases (93). 

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