Histidine residues modification

Directing the iodination reaction toward histidine residues in proteins, as opposed to principally tyrosine modification, is possible simply by increasing the pH of the lodobeads reaction from the manufacturer s recommended pH 7.0-8.2 (Tsomides et ai, 1991). No reducing agent is required to stop the iodination reaction as is the case with chloramine-T and other methods. 

Johnson, A.R., and Dekker, E.E. (1996) Woodward s reagent K inactivation of Escherichia coli L-threo-nine dehydrogenase Increased absorbance at 340-350 nm is due to modification of cysteine and histidine residues, not aspartate or glutamate carboxyl groups. Protein Sci. 5, 382-390. 

Pathological conditions are also linked to posttranslational modifications such as oxidized histidine residues found in P-amyloid protein of Alzheimer s patients, or conformational variants in the case of prion-induced encephalopathies. The development of sensitive MS tools and proteomics techniques is playing an active role in the precise description of these mechanisms.97,98... 

The complex [Ru(NH3)5H20] has proved to be a successful reagent for the modification of metalloproteins because of its affinity to accessible surface histidine residues. The Ru(NH3)j moiety has, for example, been attached to... 

N-phosphorylation has been reported for HI and H4, modifying HI at lysine residues (N -phosphoryl lysine) and H4 at a histidine residue (1- or 3-phosphoryl histidine) [109]. The modification is acid-labile and alkali-stable, and is destroyed by acid-extraction procedures used in isolating histones. 

In the catalysis of the lyase from C. perfringens, the participation of lysine residues forming intennediary Schiff bases between enzyme and substrate molecules, and of histidine residues, has been demonstrated with the aid of photooxidation, reagents for histidine modification, and borohydride reduction in the presence of substrate.408-418 Thus, according to Frazi and coworkers,414 the lyase belongs to the class I lyases (aldolases). The catalytic mechanism proposed is outlined in Scheme 3. Evidence has been educed for the existence of a similar mechanism of cleavage of sialic acid by the lyase enriched from pig kidney.411... 

The histidine residue in position 12 is crucial for activity. Its destruction by photooxidation or modification by iodination (No. 13, Table XIB) or carboxymethylation in the 3 position on the ring (No. 24, Table XIA) all destroy potential activity. The first two also substantially lower the association constant while the latter has no effect or may even increase it slightly. The CM group in the 3 position is, of course, easily accommodated and the interaction of the free carboxyl group with other positive charges nearby, e.g., His 119, may explain the increase in association constant. Conversion to a pyrazolyl residue destroys activity but not binding (No. 19). 

Directing the iodination reaction toward histidine residues in proteins, as opposed to principally tyrosine modification, is possible simply by increasing the pH of the... 

Oxidation of two out of 13 tryptophan residues in a cellulase from Penicillium notatum resulted in a complete loss of enzymic activity (59). There was an interaction between cellobiose and tryptophan residues in the enzyme. Participation of histidine residues is also suspected in the catalytic mechanism since diazonium-l-H-tetrazole inactivated the enzyme. A xylanase from Trametes hirsuta was inactivated by N-bromosuc-cinimide and partially inactivated by N-acetylimidazole (60), indicating the possible involvement of tryptophan and tyrosine residues in the active site. As with many chemical modification experiments, it is not possible to state definitively that certain residues are involved in the active site since inactivation might be caused by conformational changes in the enzyme molecule produced by the change in properties of residues distant from the active site. However, from a summary of the available evidence it appears that, for many / -(l- 4) glycoside hydrolases, acidic and aromatic amino acid residues are involved in the catalytic site, probably at the active and binding sites, respectively. 

The presence of imidazole groups in the active site region of human carbonic anhydrase B has, in fact, been demonstrated by chemical modification. Thus, bromoacetate reacts specifically with the 3 -N of a histidine residue to give a partially active monocarboxymethyl enzyme (65). The reaction depends on the initial combination of the bromoacetate ion with the anion binding site (65,83). In a detailed study, Bradbury (83) has shown that the irreversible reaction at saturation with iodoacetate... 

Various modifications to the poly(L-lysine) dendrimer have been investigated to improve transfection efficiency, such as the replacement of terminal lysine residues with either arginine or histidine or modification of the core [211, 212],... 

Flavin-containing mitochondrial MAO-A and MAO-B catalyze the oxidative deamination of neurotransmitters, such as dopamine, serotonin, and norepinephrine in the central nervous system and peripheral tissues. The enzymes share 73% sequence homology and follow the same kinetic and chemical mechanism but have different substrate and inhibitor specificities. Chemical modification experiments provide evidence that a histidine residue is essential for the catalysis. There is also strong evidence that two cysteine residues are present in the active site of MAO. 

MF Roberts, RA Deems, TC Mincey, EA Dennis. Chemical modification of the histidine residue in phospholipase A2 (Naja naja naja). A case of half-site reactivity. J Biol Chem 252 2405-2411, 1977. 

Levine, R. L. (1983). Oxidative modification of glutamine synthetase. I. Inactivation is due to loss of one histidine residue.. Biol. Chem. 258, 11823—11827. 

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