Platinum complexes and pyruvate kinase activity

The interaction of platinum complexes with bovine heart pyruvate kinase (PK) was studied by absorption, CD, fluorescence spectroscopy and enzymic activity test. Our results showed that activity of PK was reduced by cis-DDP and potassium tetrachloroplatinate in a time-and concentration dependent manner. Cis-DDP was less effective than K2PtCl4 in reducing PK activity. The native enzyme showed well defined negative Cotton effect at 222 and 208 nm indicating the presence of alpha-helical and beta structure. Platinum binding lowered the Cotton effect in this region by about 10-20% and 30-50% for the system with cis-DDP and K2PtCl4, respectively. Fluorescence study showed that platinum binding quenched tryptophan fluorescence suggesting that binding occurs at the tryptophan residue or its proximity. PK modifications induced by platinum binding would result in a greater resistance to denaturing agents.

Interaction of tetra-mu-acetatodirhodium(II) with human serum albumin

The interaction of Rh2(OAc)4 with human serum albumin (HSA) has been studied by absorption difference spectroscopy, CD spectroscopy, and quantitative precipitating HSA-antibody test. Our results demonstrate that this rhodium complex reacts easily with HSA at several ratios of reagents. The Rh atoms are coordinated to protein molecules via the imidazole rings of His residues. The structural studies have shown the conformational change of HSA modified by rhodium. Rhodium binding lowers the helicity of the native protein between 8 to 18% depending upon the molar ratios (from 1:1 to 10:1). Denaturation measurements of free HSA and HSA in the presence of dirhodium(II) acetate complex with 8-M urea followed by CD spectroscopy, suggest that rhodium affects the secondary protein structure and might stabilize HSA against denaturing agents. 8-M urea caused the unfolding of the native HSA secondary structure by about 40% and the structure of Rh(OAc)4-HSA by about 10%. The modification of native HSA by rhodium causes its decreased ability to precipitate with HSA antibodies. The decrease of antigenic properties can be connected with the unfolding of the antigen structure, which brings about perturbation of complementarity of the antigen-antibody reactive sites.

Impact of K2PtCl4 on the structure of human serum albumin and its binding ability of heme and bilirubin

Absorption, CD, gel-filtration chromatography, and immunological tests were used to evaluate the interactions of K2PtCl4 with human serum albumin. Multidentate coordination of Pt(II) to HSA causes distinct variations in the protein conformation including a considerable decrease of the helical structure. The high excess of Pt(II) ions leads to dimerization of the protein. The metal ion binding weakness the interactions of HSA with other molecules like heme or bilirubin.

Influence of aspirin and iron(III) tetrasulfonated phthalocyanine on bilirubin binding by human serum albumin

The interaction of bilirubin with aspirin-modified human serum albumin (HSA) and the influence of iron tetrasulfonated phthalocyanine on bilirubin binding by the native protein has been studied by difference spectroscopy and circular dichroism measurements. Spectroscopic studies of the systems containing bilirubin and aspirin-modified HSA compared to the analogous systems with the native protein have shown that selective acetylation of albumin at lysine 199 inhibits bilirubin binding by this protein. In both cases, interaction between bilirubin and albumin leads to complex formation at a molar ratio of ligand to protein of 2:1. The studies of the reaction of bilirubin with fragments of albumin produced by reaction with CNBr have demonstrated that one of the strong bilirubin binding sites is located in the M fragment and is close to the high-affinity binding site of aspirin. The other one was found in fragment C. Acetylation of albumin brings about marked conformational change in the protein, which probably accounts for the decrease in its ability to react with anti-HSA antibody. Bilirubin does not change the secondary structure of albumin but, like aspirin, lowers its antigenicity. It has been suggested that the decrease in antigenic properties in this case results from cooperation of the closely neighboring antigenic and bilirubin-binding sites. The studies of the influence of iron(III) tetrasulfonated phthalocyanine on bilirubin binding by HSA suggest that there is no competition between strong sites for iron(III) tetrasulfonated phthalocyanine and bilirubin, but these compounds compete for some of the weaker sites.

Structural studies of iron and cobalt tetrasulfonated phthalocyanine-globin complexes

The structure of the complexes of iron and cobalt tetrasulfonated phthalocyanines with globin has been investigated by circular dichroism (CD), electron paramagnetic resonance (EPR) and polyacrylamide gel electrophoresis. Electrophoretic investigations and the molecular weight estimation indicates that the model complexes in the solutions are dimers. It is evident from the results of CD measurements that the incorporation of the iron or cobalt tetrasulfonated phthalocyanine into apohemoglobin significantly increases the helical structure of the protein and causes an appearance of the induced Soret and visible Cotton effects. Unlike methemoglobin, several discrete transition energies in the CD Soret band of Fe(III)L-globin are observed which suggest an inequivalence of the subunits within this complex. This suggestion is supported by EPR studies, which show that the iron atoms in Fe(III)L-globin are in two low electronic states. Electronic structures of the cobalt ions in Co(II)L-globin and oxyCo(II)L-globin are similar to those of coboglobin and oxycoboglobin, respectively, as is proved by EPR results. On this basis we conclude that the oxygen adduct of Co(II)L-globin can be described as a superoxide ion corrdinated to a formally cobaltic phthalocyanine compound.

Complexes of metal phthalocyanines with globin as the models of heme proteins

The reaction between iron and cobalt tetrasulfonated phthalocyanines and globin results in the formation of the green complexes, as has been proved by difference spectroscopy. Spectrophotometric titration data indicate the formation of those complexes at the molar ratio 1:1. The complexes of ferrous, ferric and cobaltous tetrasulfonated phthalocyanines with globin have been isolated from the reaction mixtures by separation on Sephadex G-50 and precipitation of the protein fractions with ammonium sulfate. The visible spectra of these complexes are characterised by the main intensive peak at 641 nm, 678 nm, and 675 nm for ferric, ferrous and cobaltous derivatives, respectively. The new globin complexes have the property of reversible combination with oxygen and coordination with cyanide ions. It is evidence from the results of the spectrophotometric titrations of hemoglobin and methemoglobin with cobaltous tetrasulfonated phthalocyanine that iron protoporphyrins are displaced by this cobalt derivative; this suggests that phthalocyanine and porphyrin are bonded in a similar manner.