Threonine isoleucine

Amino acids that give rise to ketone bodies (acetylCoA or acetoacetyl-CoA, neither of which can bring about net glucose production) are called ketogenic amino acids. Leucine and lysine are ketogenic amino acids. Some amino acids, e.g. threonine, isoleucine, phenylalanine, tyrosine and tryptophan, can be both ketogenic and glycogenic. 

Probably the most common and widespread control mechanisms in cells are allosteric inhibition and allosteric activation. These mechanisms are incorporated into metabolic pathways in many ways, the most frequent being feedback inhibition. This occurs when an end product of a metabolic sequence accumulates and turns off one or more enzymes needed for its own formation. It is often the first enzyme unique to the specific biosynthetic pathway for the product that is inhibited. When a cell makes two or more isoenzymes, only one of them may be inhibited by a particular product. For example, in Fig. 11-1 product P inhibits just one of the two isoenzymes that catalyzes conversion of A to B the other is controlled by an enzyme modification reaction. In bacteria such as E. coli, three isoenzymes, which are labeled I, II, and III in Fig. 11-3, convert aspartate to (3-aspartyl phosphate, the precursor to the end products threonine, isoleucine, methionine, and lysine. Each product inhibits only one of the isoenzymes as shown in the figure. 

Figure 11-3 Feedback inhibition of enzymes involved in the biosynthesis of threonine, isoleucine, methionine, and lysine in E. coli. These amino acids all arise from L-aspartate, which is formed from oxaloacetate generated by the biosynthetic reactions of the citric acid cycle (Fig. 10-6). Allosteric inhibition. Q Repression of transcription of the enzyme or of its synthesis on ribosomes.

The 4-carbon aspartate molecule is the starting point for synthesis of pyrimidines and of the amino acids lysine, methionine, threonine, isoleucine, and... 

GS, and MDH were increased by HEf treatment of 1.79,1.50, and 1.49-fold, respectively. As a consequence of the increased activity of these enzymes, an increase in the amount of methionine, threonine, isoleucine, and lysine, amino acids derived from the oxalacetate pathway, were found. 

Protein concentration in maize is normally about 85 g/kg but the protein is not well balanced in AA content, with lysine, threonine, isoleucine and tryptophan being limiting. Varieties such as Opaque-2 and Floury-2 have improved AA profiles but do not appear to yield as well as conventional varieties. As a result, they are not grown extensively. Producers wishing to use such varieties should check their acceptability with the organic certifying agency. 

Amino acids with a second asymmetric center, threonine, isoleucine, and hydroxyproline, must also be taken into account, but in view of the low rotations of the first (Schellman, 1960) and the relatively infrequent occurrence of all three, they do not affect protein dispersions to any large extent. 

Figure 7-10. Amino acids that can be converted to succinyl CoA. The amino acids methionine, threonine, isoleucine, and valine, which form succinyl CoA via methylmalonyl CoA, are all essential. The carbons of serine are converted to cysteine and do not form succinyl CoA by this pathway. A defect in cystathionine synthase (M) causes homocystinuria. SAM= S-adenosylmethionine PLP = pyridoxal phosphate.

Four amino acids (lysine, threonine, isoleucine, and tryptophan) can form acetyl CoA, and phenylalanine and tyrosine form acetoacetate. Leucine is degraded to form both acetyl CoA and acetoacetate. 

More recently, Henning and Ammon (H19) described 10 aliphatic keto and aldehydic adds in normal urine. In addition to a-ketoglutaric, oxalacetic, pyruvic, glyoxylic, and a-ketoisocaproic acids, they found hydroxypyruvic, a-keto-y-methylthiobutyric, a-keto-fi-hydroxybutyric, a-keto-P-methylvaleric and a-keto-n-butyric acids, that is to say, the keto acids corresponding, respectively, to serine, methionine, threonine, isoleucine, and a-amino-n-butyric acid. They conclude that one finds in normal human urine the keto acids corresponding to all the amino adds normally present in urine, with the exception of those correspond-... 

Salmine Sulfate. A protamine found in the sperm of salmon. Contains arginine, proline, serine, glycine, valine, leucine, alanine, threonine, isoleucine, lysine, histidine, aspartic and glutamic acids. Mol wt 6000 to 7000. N about 25%. Prepn and properties Fisher, Scott, J. Pharmacol. Exp. Ther. 58, 78 (1936) Felix. Am. Sci. 43, 431 (1955) Callanan et al., J. Biol Chem 229, 279 (1957) Carroll er al, ibid. 234, 2314 (1959). Separation of components and amino add sequence of major component Ando, Watanabe, Ini. J, Protein Res. 1, 221 (1969). 

Aspartate is involved in the control point of pyrimidine biosynthesis (Reaction 1 below), in transamination reactions (Reaction 2 below), interconversions with asparagine (reactions 3 and 4), in the metabolic pathway leading to AMP (reaction 5 below), in the urea cycle (reactions 2 and 8 below), IMP de novo biosynthesis, and is a precursor to homoserine, threonine, isoleucine, and methionine (reaction 7 below). It is also involved in the malate aspartate shuttle. 

L-Homoserine is found in many tissues as a intermediate in amino acid metabolism, including threonine, isoleucine, and methionine. Catabolism of aspartate to homoserine is shown here. The biosynthetic pathway from homoserine to methionine is shown in Figure 21.6. 

Aspartyl-phosphate is an intermediate in the conversion of aspartate to homoserine (see here) in the pathway leading to biosynthesis of threonine, isoleucine, and methionine. 

In addition to methionine, threonine, isoleucine, and valine (see Fig. 39.14), the last three carbons at the chain fatty acids, form succinyl CoA by this route (see Chapter 23)... 

Bradbury et al. [16] have suggested that the cuticle of human hair contains more cystine, cysteic acid, proline, serine, threonine, isoleucine, methionine, leucine, tyrosine, phenylalanine, and arginine than does whole fiber. Data calculated from Bradbury s results and those of Robbins and Kelly [12] on whole human hair fibers are summarized in Table 2-7. Lustig and Kondritzer [18] have described comparative cuticle and cuticle-free hair analyses of certain amino acids in human hair, and their data are qualitatively similar to those of Bradbury. In addition, these authors suggest less tryptophan and histidine in cuticle than in whole fiber. 

L-Amino acids are the naturally occurring form both in proteins and as free amino acids, and the ability of different experimental animals to use different optical isomers of the amino acids has been studied. The chick is only able to use the L-form of threonine, isoleucine and valine but can use D- and L-leucine equally. It can use both D- and L-tryptophan, although the D-form is less effective (see Fisher, 1954). This probably relates to the presence of specific racemases that enable certain D- and L-interconversions to take place. Factors that affect the requirements for specific amino acids which are particularly pronounced in avian species are summarised in Table 2.3. 

The values of digestible amino acids in the intestine were calculated using the method proposed by Rulquin et al. (2001a and b). The values indicated in the present tables are not exactly the same as the values published in previous tables since the values of crude protein, amino acids, nitrogen degradability and RUP digestibility (TId) have all been updated. Nine essential amino acids have been taken into account lysine, methionine, leucine, histidine, phenylalanine, threonine, isoleucine, valine and arginine. 

In addition to the major elfectors (AdoMet, threonine, and lysine), cysteine and isoleucine may participate in the control of methionine biosynthesis, at least in some plants. Both isoleucine and cysteine would be expected to accumulate as a result of the diversion of O-phosphohomoserine toward threonine. Isoleucine is a potent competitive inhibitor of the homoserine kinase of pea seedlings (Thoenef aL, 1978), but not that of barley seedlings (Aarnes, 1976). Cysteine inhibits homoserine dehydrogenase (see Bryan, this volume. Chapter 11) and can inhibit the stimulation by AdoMet of some (Madison and Thompson, 1976) but not all (Aarnes, 1978 Thoen et al., 1978) preparations of threonine synthase. Any regulatory effect of cysteine may, however, be of short duration since the combined mechanisms described in Section II,D for regulation of cysteine biosynthesis would be expected to restore the normal concentration of this amino acid. Details of the control of methionine biosynthesis by the major effectors AdoMet, threonine, and lysine are presented below. 

Contrary to PS, polyacrylamide is a hydrophilic polymer. This may increase the ligand exchange rate, i.e., the column efficiency. Thus on the polyacrylamide-CH2-L-pro-line-Cu(II) macroporous microspheres, the enantiomers of valine, threonine, isoleucine, serine, phenylalanine, tyrosine, tryptophan, and asparagine were completely resolved in less than 1 hr with water as the eluent. The efficiency was markedly improved. However, the methylene bridge between the ligand and the matrix was not stable under acidic and basic conditions. The same sorbent, but with a long spacer, -CH2CH20CH2CH(0H)CH2-, was prepared with L-proline content 1.76 mmol/g of dry polymer." When the polymer was soaked in 0.1 M HCl, 0.1 M NaOH or 1 M NH3, aqueous solutions, respectively, at... 

Studies on liver nucleoli after starvation have shown that the nucleoli are reduced to one-half of their size 24 hours after the onset of starvation. Two days later, they have practically vanished from the nucleus. They reappear, however, within three hours after food is given. In contrast, rat liver nucleoli enlarge after administration of a diet free of protein or deficient in any one of the essential amino acids (lysine, threonine, isoleucine, methionine, tryptophan, valine) except phenylalanine, leucine, and histidine. 

Analysis shows the presence of amino acids from 0.2% tyrosine to 30.5% glycine. The five most common amino acids are glycine, 26.4—30.5% proline, 14.8-18% hydroxr proline, 13.3-14.5% glutamic acid, 11.1-11.7% and alanine, 8.6-11.3%. The remaining amino acids in decreasing order are arginine, aspartic acid, lysine, serine, leucine, valine, phenylalanine, threonine, isoleucine, hydroxylysine, histidine, methionine, and tyrosine (Eastoe, 1967 Eastoe, 1955). 

Harper, 1968 Lang, 1970) for this variation. In Test Series II, the serum concentrations of valine and leucine were roughly in the normal range the concentrations of threonine, isoleucine and lysine were clearly above normal. Thus further corrections of the amounts of these amino acids seem to be indicated. 

The reactions leading to dihydroxy acid formation are still obscure. Much evidence has been published for the view that threonine and related four-carbon compounds (such as a-ketobutyric acid) are precursors of isoleucine, and it has been postulated that one of these compounds becomes the four-carbon chain of both isoleucine and valine. " This hypothesis is untenable, however, since Ehrensvard has shown that in several microorganisms the carbon skeletons of threonine, isoleucine, and valine are derived from acetate as follows, when the organisms are grown aerobically on C HaC OOH as the sole carbon source (Fig. 4) ... 

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