Isoleucine table

Several plant aspartate kinases are activated by other amino acids such as valine, alanine, and isoleucine (Table HI). Activation does not appear to be a general effect of hydrophobic amino acids, since neither methionine nor leucine influence the activity of the maize enzyme yet, leucine has been reported to activate the enzyme isolated from Sinapsis alba and inhibit the enzyme from Helianthus annus. Interaction of these secondary effectors with the various aspartate kinases has not been fully explored, but several observations suggest a considerable degree of complexity. Alanine partially relieves threonine inhibition of the enzyme isolated from pea seedlings (Aames and Rognes, 1974). Lysine inhibition of maize aspartokinase is diminished in the presence of isoleucine, alanine, or valine (Bryan e/ al., 1970) and threonine, even though it does not inhibit the maize enzyme, counteracts... 

The asterisk signifies an asymmetric carbon. AH of the amino acids, except glycine, have two optically active isomers designated D- or L-. Isoleucine and threonine also have centers of asymmetry at their P-carbon atoms (1,10). Protein amino acids are of the L-a-form (1,10) as illustrated in Table 1. 

However, the use of a HPLC separation step enabled a remarkable acceleration of the deconvolution process. Instead of preparing all of the sublibraries, the c(Arg-Lys-O-Pro-O-P-Ala) library was fractionated on a semipreparative HPLC column and three fractions as shown in Fig. 3-2 were collected and subjected to amino acid analysis. According to the analysis, the least hydrophobic fraction, which eluted first, did not contain peptides that included valine, methionine, isoleucine, leucine, tyrosine, and phenylalanine residues and also did not exhibit any separation ability for the tested racemic amino acid derivatives (Table 3-1). 

As noted by the original authors (Dorovska et al., 1972), and cited by Fersht (1985), there is an excellent linear correlation between log/ccat/KM and the Hansch hydrophobicity parameters (v) of the side chains (Fig. 9, A), except for the two branched side chains (valine and isoleucine residues). However, since the ku values for the esters do vary somewhat (Table A6.8), the values of pKrs do not correlate as strongly with ir (Fig. 9, B). Moreover, the plot shows distinct curvature which probably indicates the onset of a saturation effect due to the physical limits of the Sj binding pocket, adjacent to the enzyme s active site. Still, the points for valine and isoleucine deviate below the others, suggesting that the pocket has a relatively narrow opening. 

Fig. 9 Correlation of (A) the second order rate constants (k2 = kcatIKM) and (B) the transition stabilization (pATS) with the hydrophobicity (it) of the substituent of the amino acid residue for the cleavage of /V-acetylamino acid methyl esters by a-chymotrypsin. The open symbols are for the points for two branched residues (valine and isoleucine). Data from Table A6.8.

From the analytical point of view, it is worth noting the biogenetic pathway of 2-methylbutanoic acid starting from isoleucine [(2S)-amino-(3S)-methylpenta-noic acid]. The (S)-configuration of the precursor is expected to remain but also enzymatic racemisation (by enolisation of the intermediate 2-oxo-3-meth-ylpentanoic acid) is known from the literature. It is not surprising that in some cases 2-methylbutanoic acid is detected as an enantiomeric ratio more or less different from the expected homochiral S enantiomer (Table 17.2) [35-40]. 

Table 3.1.3 Pathologic acylglycine species detected by organic acid analysis. CoA coenzyme A, FAO fatty acid oxidation, ILE isoleucine, LEU Leucine, MCAD medium-chain acyl-CoA dehydrogenase, MET methionine,...

Table 3.2.7 Mass assignment and reference range for acylcarnitine species accumulating in fibroblast cultures following incubation with palmitate, liCa-valine, liC>>-isoleucine, and L-carnitine...

A striking feature of the genetic code is that an amino acid may be specified by more than one codon, so the code is described as degenerate. This does not suggest that the code is flawed although an amino acid may have two or more codons, each codon specifies only one amino acid. The degeneracy of the code is not uniform. Whereas methionine and tryptophan have single codons, for example, three amino acids (Leu, Ser, Arg) have six codons, five amino acids have four, isoleucine has three, and nine amino acids have two (Table 27-3). 

Amino Acids. Traces of amino acids were found in the Devonian Newton Hamilton and Marcellus Formations in a previous study (7). In the present work (Table V) small quantities of amino acids were isolated from the Marcellus shale. In both the earlier work and the present study an amino acid that chromatographed as arginine was found. Other amino acids in the Marcellus black shale are histidine( ), methionine, alanine, tyrosine, valine, leucine or isoleucine, and two unknowns, possibly including aminobutyric acid of nonprotein origin in the Newton Hamilton Formation histidine( ). Ammonia was also present in both the Marcellus and the Newton Hamilton. 

Amino acid composition of Ex-1 is shown in Table IV together with those of S-l and F-l. The amino acid composition of Ex-1 has a pattern similar to those of S-l and F-l except for minor differences in a few amino acid contents such as proline, glycine, isoleucine, and glutamic acid. 

The amino acids in Table 27.1 that have more than one stereogenic center are isoleucine and threonine. The stereogenic centers are marked with an asterisk in the structural formulas shown. 

Table 5.2 lists the amino acid molar ratios determined for LHCP from several plant sources, and compares these results with the mean values obtained for the main glycopeptide subfraction (peak I in Table 5.1) from microbubble surfactant. It can be seen from Table 5.2 that the amino acid composition of LHCP clearly resembles that of the main glycopeptide subfraction. Specifically, in both cases nonpolar residues represent a majority and near constant fraction (i.e., 59-62%) of the amino acid composition, with the relative amounts of such residues in practically all individual cases listed following the pattern glycine > leucine, alanine, valine, proline > isoleucine, phenylalanine > methionine, tryptophan (Table 5.2). Accordingly, the glycopeptide fraction of microbubble surfactant may represent a degradation product of the light-harvesting chlorophyll a/b-protein, which is well known (ref. 373-375) to be extremely widely distributed in terrestrial, freshwater, and salt-water environments (cf. ref. 379).

To stabilize the tetrapeptide to aminopeptidase activity, amide bonds were reduced to the corresponding amines. A key observation was that modification of some of these peptide bonds negated the ability of a compound to serve as a substrate unlike before, this was independent of the identity of the a amino acids. While the peptide CllhS la was a good substrate for FTase, reduction of the first two amide bonds (cysteine, and aj-isoleucine) produced compound Id which was a potent inhibitor (IC50 20 nM) but was not a substrate (Table 2).33 Reduction of only one amide bond to give compounds lb and lc was also well tolerated in terms of inhibition potency, but both compounds were now substrates for FTase. This... 

These differences in the control of the product stereochemistry have recently been investigated by molecular modeling techniques [60,154], From these studies, the relevance of the side-chain of isoleucine 476 (PDCS.c.) (Table 2) for the stereo-control during the formation of aromatic a-hydroxy ketones became obvious, since this side-chain may protect one site of the ot-carbanion/enamine 6 (Scheme 3) against the bulky aromatic cosubstrate. Nevertheless, the smaller methyl group of acetaldehyde can bind to both sites of the a-carbanion/en-amine. The preference for one of the two acetoin enantiomers has been interpre-tated in terms of different Boltzmann distributions between the two binding modes of the bound acetaldehyde [155],... 

Table 6.1 shows the relationship between the codon sequence in mRNA and its corresponding amino acid in the new protein. Because there are 64 (43) different anticodon combinations and only 20 encoded amino acids, some different anticodon sequences encode for the same amino acid. Generally, all the anticodons matching a given amino acid will have the same first two nucleotides. Exceptions are arginine, serine, and isoleucine. For example, the codon for proline will always start with CC, but the arginine codon may start with either AG or CG. The 3 end of the tRNA anticodon pairs with the 5 end of the mRNA codon. In other words, the codon and anticodon align and bind in an antiparallel fashion. 

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