L-histidine

L-histidine [71-00-1] ITistomonas ITistomomasis ITistones ITistoplasma capsulatum ITistoplasmosis ITitec heat-transfer salt ITitec Salt... 

Synthesis. Histamine [51-45-6] 2-(4-imidazolyl)ethylarnine (1) is formed by decarboxylation of histidine by the enzyme L-histidine decarboxylase (Fig. 1). Most histamine is stored preformed in cytoplasmic granules of mast cells and basophils. In humans mast cells are found in the loose connective tissue of all organs, especially around blood and lymphatic vessels and nerves. These cells are most abundant in the organs expressing allergic diseases the skin, respiratory tract, and gastrointestinal tract. 

Histamine AND histamine antagonists). It is formed from histidine by the enzyme L-histidine decarboxylase. In the periphery, histamine is stored ia mast cells, basophils, cells of the gastric mucosa, and epidermal cells. In the CNS, histamine is released from nerve cells and acts as a neurotransmitter. The actions of histamine ate terrninated by methylation and subsequent oxidation via the enzymes histamine-/V-methyltransferase and monoamine oxidase. 

A/- -toluene su1fony1)-T-phenylalanine (62), L-histidine methyl ester (63), A/-acetyl L-valine /-butyl amide (64), etc, are used as chiral addends. 

Manometric determiaation of L-lysiae, L-argioine, L-leuciae, L-ornithine, L-tyrosiae, L-histidine, L-glutamic acid, and L-aspartic acid has been reviewed (136). This method depends on the measurement of the carbon dioxide released by the T.-amino acid decarboxylase which is specific to each amino acid. 

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). 

Furthermore, rwri-/ -hydroxy-L-histidine can be synthesized starting from the (R)-valine derived bromoacetate (see above). The diastereomeric purity of this acid is 30 1 (desired isomer/sum of all others)100. 

The amino acid L-histidine has three acid-base equilibria, with pK, values of 1.78, 5.97, and 8.97. 

Scheme 33.—The participation of L-histidine and pyridoxol to the biosynthesis of pyramine yeast.

Histidine (h/ f 35-40) and N-o-Z-l histidine (hRf 45-50) yielded brown chromatogram zones, with a pale blue fluorescence on a dark background under long-wavelength UV light (X, = 365 nm). The detection limits lay at 20 ng substance per chromatogram zone. 

The P-alanyl dipeptides carnosine and anserine (A -methylcarnosine) (Figure 31-2) activate myosin ATPase, chelate copper, and enhance copper uptake. P-Alanyl-imidazole buffers the pH of anaerobically contracting skeletal muscle. Biosynthesis of carnosine is catalyzed by carnosine synthetase in a two-stage reaction that involves initial formation of an enzyme-bound acyl-adenylate of P-alanine and subsequent transfer of the P-alanyl moiety to L-histidine. 

Hydrolysis of carnosine to p-alanine and L-histidine is catalyzed by carnosinase. The heritable disorder carnosinase deficiency is characterized by carnosinuria. 

Formation of a 2 1 L-histidine Au(III) complex is suggested on the basis of multiinstrumental techniques the N1 of the imidazole ring and the nitrogen of the a-amino group are likely involved in the coordination [66]. 

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