Involvement of glutamic acid 278 in the redox reaction of the cytochrome c oxidase from Paracoccus denitrificans investigated by FTIR spectroscopy

The molecular processes concomitant with the redox reactions of wild-type and mutant cytochrome c oxidase from Paracoccus denitrificans were analyzed by a combination of protein electrochemistry and Fourier transform infrared (FTIR) difference spectroscopy. Oxidized-minus-reduced FTIR difference spectra in the mid-infrared (4000-1000 cm-1) reflecting full or stepwise oxidation and reduction of the respective cofactor(s) were obtained. In the 1800-1000 cm-1 range, these FTIR difference spectra reflect changes of the polypeptide backbone geometry in the amide I (ca. 1620-1680 cm-1) and amide II (ca. 1560-1540 cm-1) region in response to the redox transition of the cofactor(s). In addition, several modes in the 1600-1200 cm-1 range can be tentatively attributed to heme modes. A peak at 1746 cm-1 associated with the oxidized form and a peak at 1734 cm-1 associated with the reduced form were previously discussed by us as proton transfer between Asp or Glu side chain modes in the course of the redox reaction of the enzyme [Hellwig, P., Rost, B., Kaiser, U., Ostermeier, C., Michel, H., and M?ntele, W. (1996) FEBS Lett. 385, 53-57]. These signals were resolved into several components associated with the oxidation of different cofactors. For a stepwise potential titration from the fully reduced state (-0.5 V) to the fully oxidized state (+0.5 V), a small component at 1738 cm-1 develops in the potential range of approximately +0.15 V and disappears at more positive potentials while the main component at 1746 cm-1 appears in the range of approximately +0.20 V (all potentials quoted vs Ag/AgCl/3 M KCl). This observation clearly indicates two different ionizable residues involved in redox-induced proton transfer. The major component at 1746 cm-1 is completely lost in the FTIR difference spectra of the Glu 278 Gln mutant enzyme. In the spectrum of the subunit I Glu 278 Asp mutant enzyme, the major component of the discussed difference band is lost. In contrast, the complete difference signal of the wild-type enzyme is preserved in the Asp 124 Asn, Asp 124 Ser, and Asp 399 Asn variants, which are critical residues in the discussed proton pump channel as suggested from structure and mutagenesis experiments. On the basis of these difference spectra of mutants, we present further evidence that glutamic acid 278 in subunit I is a crucial residue for the redox reaction. Potential titrations performed simultaneously for the IR and for the UV/VIS indicate that the signal related to Glu 278 is coupled to the electron transfer to/from heme a; however, additional involvement of CuB electron transfer cannot be excluded.     

Hypochlorite reacts with an organic hydroperoxide forming free radicals, but not singlet oxygen, and thus initiates lipid peroxidation

The mechanism of the reaction of hypochlorite with t-butyl hydroperoxide as a model organic hydroperoxide was studied. The reaction produces chemiluminescence with rate constant 13 +/- 2 mM-1.sec-1. The chemiluminescence of this reaction was compared with that of the hypochlorite reaction with H2O2 where singlet oxygen (1O2) is formed. In the hypochlorite reaction with H2O2, the effect of hypochlorite concentration on the integrated chemiluminescence intensity is quadratic: a red filter with transmission > 600 nm did not significantly decrease the chemiluminescence intensity: substitution of D2O for H2O increased the luminescence intensity 10-fold; infrared monomol emission was observed at 1270 nm. These results confirm the formation of 1O2 during the hypochlorite reaction with H2O2. However, when t-butyl hydroperoxide was used instead of H2O2, the concentration effect significantly differed from quadratic, and the red filter decreased the luminescence intensity by approximately 99%; D2O slightly decreased the luminescence intensity. Finally, addition of t-butyl hydroperoxide to hypochlorite was not associated with monomol emission of 1O2 in the infrared region. The data exclude the possibility of singlet oxygen formation in the hypochlorite reaction with the organic hydroperoxide. According to 1H-NMR spectroscopy, di-t-butyl peroxide is the main product of the hypochlorite reaction with t-butyl hydroperoxide; its production can be explained by radical formation, i.e., by generation of t-butyloxy radical. t-Butyl hydroperoxide and cumene hydroperoxide promoted hypochlorite-induced lipid peroxidation of phospholipid liposomes. The free radical scavenger butylated hydroxytoluene completely inhibited this effect. The data suggest that organic hydroperoxides, always present in certain amounts in vivo, may be the intermediates that interact with hypochlorite-forming free radicals which are initiators of lipid peroxidation.     

Diagnosis of Trypanosoma evansi in Saudi Arabian camels (Camelus dromedarius) by the passive haemagglutination test and Ag-ELISA

The passive haemagglutination test and Ag-ELISA were employed to monitor antibody titres and antigenaemia levels in 4 Najdi camels experimentally infected with Trypanosoma evansi. The two tests were also used to determine the prevalence of trypanosomiasis in a total of 218 Najdi camels in the Gassim region, Central Saudi Arabia, during the period from October 1992 to September 1993. Trypanosoma evansi antibodies in the experimentally infected camels rose after 14-21 days and reached a maximum of between 1:64 and 1:128 by the 12th week post infection. Circulating antigens were detected in the experimentally infected camels one week post infection and antigenaemia levels fluctuated but generally remained above preinfection OD values. The results obtained from the field survey showed that 5.5% of the sampled camels were parasitologically positive for trypanosomes, while 19.7% were serologically positive by the passive haemagglutination test and 13.8% by Ag-ELISA. No significant age difference in seropositivity was observed in the tested camels.     

Structure of a highly acidic O-specific polysaccharide of lipopolysaccharide of Pseudoalteromonas haloplanktis KMM 223 (44-1) containing L-iduronic acid and D-QuiNHb4NHb

An acidic O-specific polysaccharide was obtained by mild acid degradation of the lipopolysaccharide isolated by phenol-water extraction of Pseudoalteromonas haloplanktis strain KMM 223 (44-1). L-Iduronic acid (IdoA) was found to be a component of the polysaccharide and identified by NMR spectroscopy and after carboxyl-reduction followed by acid hydrolysis and acetylation, by GLC-MS as 2,3,4-tri-O-acetyl-1,6-anhydroidose. On the basis of 1H and 13C NMR spectroscopic studies, including 1D NOE, 2D NOESY, HSQC and HMBC experiments, the following structure of the branched pentasaccharide repeating unit of the polysaccharide was established: -->4)-beta-D-GlcpAI-(1-->4)-beta-D-GlcpAII-(1-->3)-beta-D-++ +QuipNHb4NHbII- (1-->2)-alpha-L-IdopA-(-->4 increases 1 alpha-D-QuipNAc4NAcI where QuiNAc4NAc and QuiNHb4NHb are 2,4-diacetamido-2,4,6-trideoxyglucose and 2,4,6-tri-deoxy-2,4- di[(S)-3-hydroxybutyramido]glucose, respectively. This is the first report of L-iduronic acid in a lipopolysaccharide and of D-QuiNHb4NHb in nature.     

Electron transport in hot pressed Y3−x Gd x Fe5O12

Electron transport properties of a few hot-pressed garnets of the series Y_3−xGd_xFe₅O₁₂ (wherex=0, 1 and 2·4) have been measured. For comparison, a normal sintered YIG has been studied to see the effect of porosity and microstructure. The electron transport properties have been discussed on the basis of the model suggested by Austin and Mott keeping in view the distortion caused by the substitution.     

The influence of the central region containing residues 19-25 on the aggregation properties and secondary structure of Alzheimer's beta-amyloid peptide

Alzheimer's beta-amyloid peptide (Abeta) is a 39- to 43-amino-acid peptide that is the major component of neuritic plaques found in Alzheimer's disease (AD). The central region of Abeta plays a crucial role in many of its properties, including aggregation, neurotoxicity, proteolytic processing and interactions with other proteins, such as apolipoprotein E. Two mutations in this region, Ala21-->Gly and Glu22-->Gln, give rise to early onset forms of disease. We have studied several peptides based on the central region of Abeta in order to clarify the influence of specific amino acid residues on physicochemical behaviour. To avoid difficulties due to oxidation of Met35, the latter was replaced by the amino acid isostere, norleucine (Ahx), giving [Ahx35]Abeta-(25-35)-amide as a prototype structure. To this prototype, addition of pairs of amino acid residues from the sequence of Abeta, forming the corresponding 23-, 21- and 19-35 derivatives, resulted in peptides that aggregated to form fibrils of diameter 6-10 nm. The rate of aggregation was more rapid as peptide length increased. Circular dichroism spectra of aged solutions of peptides revealed that aggregation was accompanied by a transition from random structure to beta sheet for some, but not all, peptides. The mutation from Ala to Gly at position 21 increased the rate of aggregation and altered the tendency to adopt secondary structure in the direction away from alpha helix and towards beta sheet. In individuals with the Ala21-->Gly mutation, these results would suggest that truncated species with N-termini in the region containing residues 17-20 would be more amyloidogenic than the wild type homologues.