Histidine copper chelates with

The catalase-like action of hemocyanin is probably because of copper bound to one or more amino acids in the protein. Contrary to previous claims (12), arginine chelates with copper are not the only catalytically active species. For example, copper chelates with histidine and histamine are also active. The rates appear to be a first power function of copper and H202. Studies now being carried out with V. S. Sharma in our laboratories indicate that the active species is the Cu (II) L form where L represents the ligand. The copper chelate forms a ternary complex with... 

Mn2+, D.F.P.-ase is further activated by cysteine, histidine, thiolhistidine, and serine, histamine and 2 2 -dipyridyl. Reagents reacting with metal ions, SH groups and carbonyl groups inhibit D.F.P.-ase activity. Work is proceeding on the further elucidation of such mechanisms.1 In a somewhat similar connexion attention is called to the fact that the non-enzymic hydrolysis of D.F.P. is accelerated by heavy metals and their complexes, in particular by copper chelates of ethylene diamine, o-phenanthroline, 2 2 -dipyridyl and histidine.2... 

The copper(II) ion as well as a number of copper(II) chelates with incompletely filled coordination shells, e.g., the 1 1 chelates of 2,2 -dipyri-dyl, 1,10-phenanthroline, ethylenediamine, or histidine, were found to increase the rate of hydrolysis of diisopropylphosphorofluoridate, a cholin-... 

The most effective catalysts were found to be the 1 1 copper complexes with a,a -dipyridyl, L-histidine, o-phenanthroline, imidazole, and ethylene-diamine. Because of the apparent requirement that the metal be incompletely coordinated, it was suggested that the reactive positions of the metal are those occupied by water or hydroxide ion. Three such species have been reported by Fowkes et al. (9) from a study of aqueous equilibria involving the 1 1 dipyridyl chelate, according to the following reaction scheme ... 

P(NIPAAm-co-l-VIA) copolymers to purify histidine-tagged green flourescent protein (His-tag GFP) from recombinant E. colt by copper-chelate affinity precipitation. The authors noted that the comonomer distribution in the copolymer played a critical role in the interaction between the copolymer and the His-tag GFP, wlrile complete elution of the affinity-bound Gu P(NIPAAm-co-l-VIA) was achieved with PLC comonomer sequences (imidazole groups exposed to the outer solution), no recovery was obtained with IMAC nonbound copolymer fraction (imidazole groups unexposed). More details pertaining to the behavior of these systems can be found in a review by Lozinsky. ... 

Various spectroscopic methods have been used to probe the nature of the copper centers in the members of the blue copper oxidase family of proteins (e.g. see ref. 13). Prior to the X-ray determination of the structure of ascorbate oxidase in 1989, similarities in the EPR and UV-vis absorption spectra for the blue multi-copper oxidases including laccase and ceruloplasmin had been observed [14] and a number of general conclusions made for the copper centers in ceruloplasmin as shown in Table 1 [13,15]. It was known that six copper atoms were nondialyzable and not available to chelation directly by dithiocarbamate and these coppers were assumed to be tightly bound and/or buried in the protein. Two of the coppers have absorbance maxima around 610 nm and these were interpreted as blue type I coppers with cysteine and histidine ligands, and responsible for the pronounced color of the protein. However, they are not equivalent and one of them, thought to be involved in enzymatic activity, is reduced and reoxidized at a faster rate than the second (e.g. see ref. 16). There was general concurrence that there are two type HI... 

Substantial rate accelerations are observed in these systems for base hydrolysis. Thus for the ethylenediamine complex (18) rate increases of 4x 104 for GlyOEt to 1.4 x 107 for ethyl picolinate are observed.85 These rate accelerations are consistent with the formation of carbonyl-bonded species (18). The effects with methyl L-cysteinate and methyl L-histidinate are much less marked as such ligands can give mixed ligand complexes which do not involve alkoxycarbonyl donors. Thus in the case of methyl L-histidinate the complex (20) is formed. For these latter two esters only relatively small rate accelerations of 20-100 occur. For the chelate ester complexes, the ratios of kcm/kH2o fail within the range 3.8 x 109 to 3.2 x 1011. Such values for the relative nucleophilicity of water and hydroxide ion are comparable with those previously noted for copper(II) complexes.82... 

These observations are also consistent with copper complex modulation of A terminal desaturase activity [702]. A purified chicken liver microsomal preparation of stearoyl-CoA A -desaturase was inhibited with Cu(IIXtyrosi-nate)j, Cu(II)(lysinate)2 and Cu(II)(histidinate)2. These chelates lowered the steady-state level of ferrocytochrome only 20% and only partially inhibited the NADH-ferricyanide reductase activity, indicating that the terminal desaturation step was being inhibited. Since oxygen is known to be involved in this desaturation and that there is an initial reduction of the desaturase iron, it is plausible that these chelates are decreasing desaturase activity by acting as superoxide scavengers [702]. 

Primary effect affinity precipitation is best suited for the purification of proteins showing multiple-point interaction with some of the above mentioned small affinity ligands. Typical target substances for primary effect affinity precipitation are, for example, enzymes, which interact with triazine dyes such as Cibacron blue, but also proteins rich in surface histidine residues, since these protein show strong interaction with immobilized (chelated) transition metal ions such as copper or zinc. The latter effect can be used in a very general manner since the introduction of so-called histidine-tags (i.e., multiple histidine sites) into recombinant proteins is a routine procedure, which normally has litde or no influence on the biological activity of the protein. ... 

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