Amino-acid residues threonine

Human insulin differs from bovine insulin at only three amino acid residues Threonine replaces alanine once in the A chain (residue 8) and once in the B chain (residue 30), and isoleucine replaces valine once in the A chain (residue 10). Insulins from most mammals have similar structures. 

FIGURE 5.5 (a) The hydroxy amino acids serine and threonine are slowly destroyed during the course of protein hydrolysis for amino acid composition analysis. Extrapolation of the data back to time zero allows an accurate estimation of the amonnt of these amino acids originally present in the protein sample, (b) Peptide bonds involving hydrophobic amino acid residues snch as valine and isolencine resist hydrolysis by HCl. With time, these amino acids are released and their free concentrations approach a limiting value that can be approximated with reliability. 

It is a peptide containing 27 amino acid residues containing the amino acids L-histidine (His) L-aspartic acid (Asp) L-serine (Ser) glycine (Gly) L-threonine (Thr) L-phenyl-alanine (Phe) L-glutamic acid (Glu) L-glutamine [Glu(NHj)] L-leucine (Leu) L-arginine (Arg) L-alanine (Ala) and L-valinamide (Va -NHj). 

In addition, eNOS is subject to protein phosphorylation. It can be phosphotylated on several serine (Ser), threonine (Thr), and tyrosine (Tyr) residues however, major changes in enzyme function have been reported for the phosphorylation of amino acid residues Seri 177 and Thr495 (in the human eNOS sequence) (Fig. 3). 

On the other hand, resonance assignments for CP of threonine and serine, and C and Cy of hydroxy proline, were difficult to make, because of their proximity to carbohydrate carbon resonances. In most cases then, the resonances were assigned on the basis of the effects of pH on the chemical shifts of those resonances. It was shown that the chemical shifts for the carbohydrate carbon resonances were virtually unaffected (AS 0.4 p.p.m.) when going from the cationic state (pH 2) to the anionic state (pH 11) of the amino acid residues. The chemical shifts of C and CP of the amino acid residues, however, shifted considerably (up to 3.1 and 6.6 p.p.m. for C" and CP, respectively see Table VI). 

There are several subfamilies of PKs, which either require Ca2+, diacyl glycerol or phorbol esters or extracellular agonists for activation. Four major groups of PKs are distinguished. Basic amino acid-directed kinases (PKA, PKB, PKC) phophorylate serine/threonine around such amino acid residues. PKA is activat-... 

By means of a procedure described above, Hanson and Fittkau (HI) isolated seventeen different peptides from normal urine. One of them, not belonging to the main peptide fraction, consisted of glutamic acid, and phenylalanine with alanine as the third not definitely established component. The remaining peptides contained five to ten different amino acid residues and some unidentified ninhydrin-positive constituents. Four amino acids, i.e., glutamic acid, aspartic acid, glycine, and alanine, were found in the majority of the peptides analyzed. Twelve peptides contained lysine and eight valine. Less frequently encountered were serine, threonine, tyrosine, leucine, phenylalanine, proline, hydroxyproline, and a-aminobutyric acid (found only in two cases). The amino acid composi-... 

Figure 3.6 Protein kinases. Selected amino acid residues within proteins are targets for kinases, (a) Tyrosine kinase reaction, (b) Serine/threonine kinase...

This peptide is also referred to as apo Lp-Ser based on its COOH-terminal amino acid residue (H4, Ml), initially believed to be valine (B8, B9). Its NH2-terminal residue is threonine with the amino acid composition listed in Table 9. The sequence of this peptide announced recently (S34) has the noted feature (Fig. 6), also shared by apo LP-Gln II (B5) and apo LP-Ala (B6) of having a number of basic adjacent to acidic residues. 

These two polypeptides have been shown to have identical amino acid composition (Table 9) but to differ from each other in sialic acid content. Da and D4 have 1 and 2 moles of sialic acid per mole of protein, respectively (A5, A6, B9, BIO, E5). A third form without sialic acid has been isolated by preparative isoelectric focusing (A5). Both D3 and D4 have the same NHa-terminal (serine) and COOH-terminal (alanine) amino acid residue and a molecular weight of about 10,000. The complete amino acid sequence has recently been announced (B6) and is reported in Fig. 7. These studies show that the polysaccharide having sialic acid as its terminal sugar, is linked to threonine 74 of the polypeptide chain. 

Figure 8.4. Amino acid sequence of porcine insulin is depicted in (a). Trypsin cleavage sites are also indicated. Trypsin therefore effectively removes the insulin carboxy-terminus B chain octapeptide. The amino acid sequence of human insulin differs from that of porcine insulin by only one amino acid residue. Porcine insulin contains an alanine residue at position 30 of the B-chain, whereas human insulin contains a threonine residue at that position. Insulin exhibiting a human amino acid sequence may thus be synthesized from porcine insulin by treating the latter with tr5q)sin, removal of the C terminus fragments, generated and replacement of this with the synthetic octapeptide shown in (b). Reproduced by permission of John Wiley Sons Ltd from Walsh Headon (1994)...

Biopharmaceuticals based on natural proteins and peptides are often called by the same name as the biologic natural material despite differences in one or more amino-acid residues. For example, insulin, which regulates blood glucose and is used clinically to treat type 1 diabetes and some cases of type 2 diabetes, has several variants that are approved for human use. Insulin contains two polypeptides, A and B chains (Figure 1.2), that are linked together by two disulfide bridges to assume a biologically active conformation. Compared with human insulin, insulin extracted from beef tissue exhibits threonine alanine and isoleucine valine substitutions at posi-... 

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