Histidine characteristics

The crude product is dissolved in five times its weight of water, and after clearing with a little Norite the solution is diluted with one and one-half volumes of 95 per cent alcohol. The product separates in well-formed, snow-white crystals, and after standing for several days in an ice chest is collected with suction on a Buchner funnel. The yield of purified histidine monohydrochloride is 75-80 g. (Note 5). The compound melts at 251-2520, with decomposition. The amino acid is not race-mized by the procedure employed, and shows the characteristic optical activity, [a]n6° = +8.00, in the presence of three moles of... 

C17-0017. Describe the acidic and basic characteristics of the amino acids histidine and threonine. 

Figure 15 presents a qualitative comparison of different oxidation types on histidine ACW. Hence, the ACP cannot be seen to be characteristic for antioxidant defense, but more likely it is a feature of prehistory connected with the free-radical processes, reflecting the degree of oxidative stress. 

Parmentier, R., Ohtsu, H., Djebbara-Hannas, Z., Valatx, J. L., Watanabe, T. and Lin, J. S. Anatomical, physiological, and pharmacological characteristics of histidine decarboxylase knock-out mice evidence for the role of brain histamine in behavioral and sleep-wake control. /. Neurosci. 22 7695-7711,2002. 

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. 

In reference 190, the authors describe the spectroscopic and X-ray crystallographic techniques they used to determine the pMMO structure. First, EPR and EX AFS experiments indicated a mononuclear, type 2 Cu(II) center hgated by histidine residues and a copper-containing cluster characterized by a 2.57 A Cu-Cu interaction. A functional iron center was also indicated by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). ICP-AES uses inductively coupled plasma to produce excited atoms that emit electromagnetic radiation at a wavelength characteristic of a particular element. The intensity of this emission is indicative of the concentration of the element (iron in this case) within the sample. 

Hb possesses both 4 and 5-coordinate forms as demonstrated by the Raman spectra (Figure 1) and the spj it Soret band of the absorption spectrum (9,36). In contrast, Mb shows only the red Soret component and the Raman lines characteristic of the 5-coordinate form. Thus, myoglobin s R-like structure favors the 5-coordinate form. The R/T difference in affinity for histidine might also be expected to reveal itself in the strength of the Ni-histidine bond. In native Fe hemoglobin, the Fe-histidine bond increases in strength upon conversion from the T to R structure (31,39). 

Characteristic amino add composi- Absence of tryptophan, histidine and arginine tion... 

There is also a conformational ambiguity characteristic of the histidine side chain as it is built into electron density maps The two possible orientations about the Cfi-Cy bond are indistinguishable, so the crystal-lographer must select one of these orientations based on chemical intuition [e.g., the availability of hydrogen bond interaction(s) in one particular orientation and not the other]. Additionally, the proper histidine tautomer is likewise selected by chemical intuition. Reynolds et al. (1973) demonstrated that the Ne-H tautomer is the predominant form of free histidine in solution, and these investigators showed that the ratio Ne-H tautomer/N8-H tautomer is approximately 80% 20% (Fig. 13). 

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