Histidine isolation

Aziridine 269 (Scheme 3.98), on treatment with pyrazole (270) and subsequent TFA deprotection, gave P-pyrazolylalanine 271, first isolated from Citrullus vulgaris (a water melon) and isosteric with histidine [148]. Treatment of 269 with 1,2,4-ox-adiazolidine-3,5-dione 272 gave (S)-quisqualic acid (273), an active ingredient of the ancient Chinese drug Shihchuntze, an anthelmintic made from the seeds of Quisqualis indica [148]. 

Pyrazol-1 -ylalanine, an isomer of histidine, was isolated from Citrullus vulgaris (watermelon) seed and its structure was confirmed by comparison with synthetic material 107). It was the major free amino acid in the dormant dry seed but was present in only trace amounts in vegetative tissue. While present in seed extracts of other members of the Cucurbitaceae, it has not been identified as occurring in members of other plant families. 

X-ray absorption spectroscopy has been performed on the isolated Rieske protein from bovine heart mitochondrial bc complex 69) as well as on the Rieske-type cluster in Burkholderia cepacia phthalate dioxygenase (PDO) (72). The analysis performed by Powers et al. 69) was significantly hampered by the fact that the presence of two histidine ligands was not fully recognized therefore, only the results obtained with the dioxygenase where the mononuclear iron has been depleted will be considered here. Table VII gives a comparison of the distances obtained from the fit of the EXAFS spectra assuming an idealized Rieske model and of the distances in the crystal structures... 

FIGURE 14-3 Synthesis and metabolism of histamine. Solid lines indicate the pathways for histamine formation and catabolism in brain. Dashed lines show additional pathways that can occur outside the nervous system. HDC, histidine decarboxylase HMT, histamine methyltransferase DAO, diamine oxidase MAO, monoamine oxidase. Aldehyde intermediates, shown in brackets, have been hypothesized but not isolated. 

Histamine synthesis in the brain is controlled by the availability of L-histidine and the activity of histidine decarboxylase. Although histamine is present in plasma, it does not penetrate the blood-brain barrier, such that histamine concentrations in the brain must be maintained by synthesis. With a value of 0.1 mmol/1 for L-histidine under physiological conditions, HDC is not saturated by histidine concentrations in the brain, an observation that explains the effectiveness of large systemic doses of this amino acid in raising the concentrations of histamine in the brain. The essential amino acid L-histidine is transported into the brain by a saturable, energy-dependent mechanism [5]. Subcellular fractionation studies show HDC to be localized in cytoplasmic fractions of isolated nerve terminals, i.e. synaptosomes. 

Bricker, T. M, J. Morvant, N. Masri, H. M. Sutton, L. K. Frankel (1998) Isolation of a highly active photosystem n preparation from Synechocystis 6803 using a histidine tagged mutant of CP 47. Biochim. Biophys. Acta, 1409 50-57... 

The advantage of such co-purification protocols is that the fully processed protein serving as the bait can allow interactions in a native environment and cellular location to allow isolation of multicomponent complexes. One limitation with this approach is the necessity for an antibody with specific immunoreactivity and immunoprecipitative capability for the bait protein. This drawback can be addressed by expression of the protein with an epitope tag. Excellent antibodies to a variety of epitope tags are available and can be utilized for immunoaffinity purification. Tags such as 6-histidine and GST allow purification using affinity characteristics to nickel and GSH beads, respectively. 

As early as 1905 Abderhalden (Al) isolated from the hydrolyzate of the nondiffusible fraction of human urine four amino acids, i.e., leucine, alanine, glycine, and glutamic acid, and detected two others phenylalanine and aspartic acid. Some amino acids derived from this fraction have been quantitatively determined by Albanese et al. (A3) who found in the amount of the nondiffusible fraction corresponding to one liter of urine as much as 32.8 mg tryptophan, 18.0 mg phenylalanine, 16.2 mg methionine, 15.2 mg cystine, 13.1 mg arginine, 6.7 mg histidine, and 3.9 mg tyrosine. 

Lactamases of classes A, C, and D are serine peptidases and as such have been discussed in Sect. 3.3. Class B /1-lactamases, in contrast, are met-allohydrolases. For example, a class B /1-lactamase isolated from Bacillus cereus was shown to contain two Zn-atoms per protein molecule, of which only one is essential for catalysis. Three histidine residues act as ligands for the first Zn2+ ion, and a fourth histidine contributes to the binding of the second Zn-atom [82] [83],... 

Affinity chromatography and related techniques (e.g., thiol chromatography and IMAC) are widely used for preparative isolation because they enable a single protein or class of proteins to be selectively purified from very complex mixtures. They may be occasionally used as analytical tools. For example, protein A affinity chromatography has been used for quantitative analysis of immunoglobulins in ascites fluid.45 Information about surface-accessible histidine and phosphate groups may be obtained using IMAC. 

The enzyme catalyzing the formation of retinal 2 by means of central cleavage of P-carotene 1 has been known to exist in many tissues for quite some time. Only recently, however, the active protein was identified in chicken intestinal mucosa (3) following an improvement of a novel isolation and purification protocol and was cloned in Escherichia coli and BHK cells (4,5). Iron was identified as the only metal ion associated with the (overexpressed) protein in a 1 1 stoichiometry and since a chromophore is absent in the protein heme coordination and/or iron complexation by tyrosine can be excluded. The structure of the catalytic center remains to be elucidated by X-ray crystallography but from the information available it was predicted that the active site contains a mononuclear iron complex presumably consisting of histidine residues. This suggestion has been confirmed by... 

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