Purification and properties of pyruvate kinase from Thermoplasma acidophilum

Thermoplasma acidophilum is a thermoacidophilic archaebacterium occupying a paradoxical place in phylogenetic trees (phenotypically it is a thermoacidophile but phylogenetically it classifies with the methanogens). To better understand its phylogeny, the pyruvate kinase from this organism is being investigated as a molecular marker. The enzyme has been purified and has a native M(r) of 250,000. It consists of four, apparently identical subunits each of M(r) 60,000. No remarkable kinetic differences have been found between this thermophilic enzyme and its mesophilic counterparts other than its greater thermostability. Its amino acid composition has been determined and some partial sequencing has been done.     

Hydrogen sulfide:A novel component in Arabidopsis peroxisomes which triggers catalase inhibition

Plant peroxisomes have the capacity to generate different reactive oxygen and nitrogen species(ROS and RNS),such as H_2O_2,superoxide radical(O_2~-),nitric oxide and peroxynitrite(ONOO~-).These organelles have an active nitrooxidative metabolism which can be exacerbated by adverse stress conditions.Hydrogen sulfide(H_2S)is a new signaling gasotransmitter which can mediate the posttranslational modification(PTM)persulfidation.We used Arabidopsis thaliana transgenic seedlings expressing cyan fluorescent protein(CFP)fused to a canonical peroxisome targeting signal 1(PTS1)to visualize peroxisomes in living cells,as well as a specific fluorescent probe which showed that peroxisomes contain H_2S.H_2S was also detected in chloroplasts under glyphosate-induced oxidative stress conditions.Peroxisomal enzyme activities,including catalase,photorespiratory H_2O_2-generating glycolate oxidase(GOX)and hydroxypyruvate reductase(HPR),were assayed in vitro with a H_2S donor.In line with the persulfidation of this enzyme,catalase activity declined significantly in the presence of the H_2S donor.To corroborate the inhibitory effect of H_2S on catalase activity,we also assayed pure catalase from bovine liver and pepper fruit-enriched samples,in which catalase activity was inhibited.Taken together,these data provide evidence of the presence of H_2S in plant peroxisomes which appears to regulate catalase activity and,consequently,the peroxisomal H_2O_2 metabolism.     

The Oxidative Inactivation of Tissue Inhibitor of Metalloproteinase-1 (TIMP-1) by Hypochlorous Acid (HOCl) is Suppressed by Anti-Rheumatic Drugs

Tissue inhibitors of metalloproteinases (TIMPs) prevent uncontrolled connective tissue destruction by limiting the activity of matrix metalloproteinases (MMPs). That TIMPs should be susceptible to oxidative inactivation is suggested by their complex tertiary structure which is dependent upon 6 disulphide bonds. We examined the oxidative inactivation of human recombinant TIMP-1 (hr TIMP-1) by HOCl and the inhibition of this process by anti-rheumatic agents.

TIMP-1 was exposed to HOCl in the presence of a variety of disease modifying anti-rheumatic drugs. TIMP-1 activity was measured by its ability to inhibit BC1 collagenase activity as measured by a fluorimetric assay using the synthetic pEptide substrate (DNP-Pro-Leu-Ala-Leu-Trp-Ala-Arg), best cleaved by MMP-1.

The neutrophil derived oxidant HOCl, but not the derived oxidant N-chlorotaurine, can inactivate TIMP-1 at concentrations achieved at sites of inflammation. Anti-rheumatic drugs have the ability to protect hrTIMP-1 from inactivation by HOCl. For D-penicil-lamine, this effect occurs at plasma levels achieved with patients taking the drug but for other anti-rheumatic drugs tested this occurs at relatively high concentrations that are unlikely to be achieved in vivo, except possibly in a microenvironment. These results are in keeping with the concept that biologically derived oxidants can potentiate tissue damage by inactivating key but susceptible protein inhibitors such as TIMP-1 which form the major local defence against MMP induced tissue breakdown.     

FBXO44 promotes DNA replication-coupled repetitive element silencing in cancer cells

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Identification of the ubiquinone-binding domain in the disulfide catalyst disulfide bond protein B.

Disulfide bond (Dsb) formation is catalyzed in the periplasm of prokaryotes by the Dsb proteins. DsbB, a key enzyme in this process, generates disulfides de novo by using the oxidizing power of quinones. To explore the mechanism of this newly described enzymatic activity, we decided to study the ubiquinone-protein interaction and identify the ubiquinone-binding domain in DsbB by cross-linking to photoactivatable quinone analogues. When purified Escherichia coli DsbB was incubated with an azidoubiquinone derivative, 3-azido-2-methyl-5-[(3)H]methoxy-6-decyl-1,4-benzoquinone ([(3)H]azido-Q), and illuminated with long wavelength UV light, the decrease in enzymatic activity correlated with the amount of 3-azido-2-methyl-5-methoxy-6-decyl-1,4-benzoquinone (azido-Q) incorporated into the protein. One azido-Q-linked peptide with a retention time of 33.5 min was obtained by high performance liquid chromatography of the V8 digest of [(3)H]azido-Q-labeled DsbB. This peptide has a partial NH(2)-terminal amino acid sequence of NH(2)-HTMLQLY corresponding to residues 91-97. This sequence occurs in the second periplasmic domain of the inner membrane protein DsbB in a loop connecting transmembrane helices 3 and 4. We propose that the quinone-binding site is within or very near to this sequence.     

DNA Sequences from Formalin-Fixed Nematodes: Integrating Molecular and Morphological Approaches to Taxonomy

To effectively integrate DNA sequence analysis and classical nematode taxonomy, we must be able to obtain DNA sequences from formalin-fixed specimens. Microdissected sections of nematodes were removed from specimens fixed in formalin, using standard protocols and without destroying morphological features. The fixed sections provided sufficient template for multiple polymerase chain reaction-based DNA sequence analyses.