In histidine

Imidazole-4-catbonitrile, 5-amino-synthesis, 5, 463 Imidazolecarboxamide, cyano-reactions, 5, 436 Imidazole-4-carboxamide Hofmann reaction, 5, 435 Imidazole-4-carboxamide, 5-amino-in histidine biosynthesis, 1, 90 reactions... 

The dinitrophenyl group has been used to protect the imidazole — NH group in histidines (45% yield)" by reaction with 2,4-dinitrofluorobenzene and potassium carbonate. Imidazole —NH groups, but not a-amino acid groups, are quantitatively regenerated by reaction with 2-mercaptoethanol (22°, pH 8, 1 h)." The 2,4-... 

The phenacyl group is stable to HBr-AcOH, CF3COOH, and CF3S03H. It is used to protect the Tr-nitrogen in histidine in order to reduce racemization during peptide bond formation. ... 

Pyrimidine and imidazole rings are particularly important in biological chemistry. Pyrimidine, for instance, is the parent ring system in cytosine, thymine, and uracil, three of the five heterocyclic amine bases found in nucleic acids An aromatic imidazole ring is present in histidine, one of the twenty amino acids found in proteins. 

Problem 24.21 What is the percent protonation of the imidazole nitrogen atom in histidine at a physiological pH of 7.3 (See Section 24.5.)... 

The 2-adamantyloxycarbonyl group has been found suitable for protection of the imidazole function in histidine during peptide synthesis.[7a]... 

Tanokura M (1983) 1 II-NMstudy R on the tautomerism of the imidazole ring of histidine residues I. Microscopic pK values and molar ratios of tautomers in histidine-containing peptides. Biochim Biophys Acta 742 576-585. 

Ohtsu, H. Watanabe, T. (2003). New functions of histamine found in histidine decarboxylase gene knockout mice. Biochem. Biophys. Res. Commun. 305, 443-7. 

Figure 3.24 (A) Labeling of side-chain atoms in histidine residues for identification...

Increased understanding of reaction mechanisms in the 1940s and 1950s pinpointed general acid or base catalysis as likely to be of importance in many hydrolytic reactions. The imidazole nucleus in histidine was the obvious center in proteins to donate or accept protons at physiological pH. The involvement of histidine was shown by photochemical oxidation in the presence of methylene blue (Weil and Buchert, 1951) which destroyed histidine and tryptophan and inactivated chymotrypsin and trypsin. 

Ghosh AK, Hirasawa N, Ohtsu H, Watanabe T, Ohuchi K Defective angiogenesis in the inflammatory granulation tissue in histidine decarboxylase-deficient mice but not in mast cell-deficient mice. J Exp Med 2002 195 973-982. 

Lactobacillus delbrueckii. In 1953, Rodwell suggested that the histidine decarboxylase of Lactobacillus 30a was not dependent upon pyridoxal phosphate (11). Rodwell based his suggestion upon the fact that the organism lost its ability to decarboxylate ornithine but retained high histidine decarboxylase activity when grown in media deficient in pyridoxine. It was not until 1965 that E. E. Snell and coworkers (12) isolated the enzyme and showed that it was, indeed, free of pyridoxal phosphate. Further advances in characterization of the enzyme were made by Riley and Snell (13) and Recsei and Snell (14) who demonstrated the existence of a pyruvoyl residue and the participation of the pyruvoyl residue in histidine catalysis by forming a Schiff base intermediate in a manner similar to pyridoxal phosphate dependent enzymes. Recent studies by Hackert et al. (15) established the subunit structure of the enzyme which is similar to the subunit structure of a pyruvoyl decarboxylase of a Micrococcus species (16). 

Figure 16.1. Schematic representation of the yeast two-hybrid system for evaluation of protein-protein interactions. Haploid yeast of a and a cells can mate to form (a/a) diploid cells. (A) If two test proteins, PT1 and PT2—expressed in (a/a) diploid cells as fusion proteins of DNA binding domains (DAB) and activation domains (AD) of yeast gene-transcript activator proteins—bind to each other, the binding interaction allows the diploid cells to grow in histidine selection media. Histidine selection media is permissive for diploid cells that express the HISS reporter gene only if PT1 and PT2 interact. (B) If PT1 and PT2 do not interact, no HISS gene product is expressed and the hybrid cell cannot grow in histidine media.

Napper, S. Delbaere, L.T.J. Waygood, E.B. The aspartyl replacement of the active site histidine in histidine-containing protein, HPr, of the Escherichia coli phosphoenolpyruvate sugar phosphotransferase system can accept and donate a phosphoryl group. Spontaneous dephosphorylation of acyl-phosphate autocatalyzes an internal cyclization. J. Biol. Chem., 274, 21776-21782 (1999)... 

The glutamine synthetase of E. coli is independently modulated by various products of glutamine metabolism (see Fig. 22-6). In this concerted inhibition, the extent of enzyme inhibition is greater than the sum of the separate inhibitions caused by each product. For E. coli grown in a medium rich in histidine, what would be the advantage of concerted inhibition ... 

The imidazole groups in histidine side chains are parts of the active sites of many enzymes. Like other basic groups in proteins they also may bind metal ions. 

Sequentially adjacent side chains may or may not be near each other as seen in the plot of the distances between successive terminal reference points, T, in Fig. 5e. For carboxyl, amide, valine, leucine, and arginine side chains, T was defined as the center between the two terminal atoms. In proline Cy was chosen, in methionine the sulfur, in threonine the oxygen, and in histidine the point between C2 and N3. 

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