Regulation of homocysteine metabolizing enzymes in Aspergillus nidulans

Summary Mutants of Aspergillus nidulans blocked in the main pathway of cysteine synthesis show an elevated level of the enzymes involved in the synthesis of cysteine from homocysteine i.e. cystathionine -synthase and -cystathionase and a depressed level of homocysteine methyltransferase. This results in a considerable change in the sulfur amino acids pool as compared to the wild type. Upon addition of cysteine to the growth medium the first two enzymes are repressed while the level of the third one increases. These data indicate that the two diverging pathways of homocysteine metabolism are anti-coordinately regulated.     

Localization of neurosecretion in the nervous system of Catenulida (Turbellaria)

Summary The nervous system of the most primitive fresh-water Turbellaria of the order Catenulida was investigated. Neurosecretory cells were found to occur in it. These cells have a structure similar to that of nerve cells, they only differ by the presence of neurosecretion granules and a more developed golgi complex. In the simplest Catenulida,Stenostomun, neurosecretory granules are found both in the brain cells and in the trunks in the nerve fibres where they are rather randomly distributed. Another representative of this family, the more highly organizedCatenula, exhibits specialized brain and nerve trunk regions containing neurosecretion granules. This work was supported in part by the Committee on Cytobiology of the Polish Academy of Sciences     

HineI is an isoschizomer of HinfIII restriction endonuclease

HineI is a restriction enzyme isolated from Haemophilus influenzae strain Re. Like other type III restriction endonucleases it requires ATP for cleavage and S-adenosyl-methionine for methylation of DNA. This enzyme recognises the same sequence as HinfIII (Piekarowicz et al., 1981) and cleaves and methylates DNA in a manner similar to all type III restriction enzymes.     

Adenosylhomocysteinase:Adenosine complex

Adenosylhomocysteinase from yellow lupin seeds forms a specific complex with adenosine. The complex can be isolated either by nonequilibrium or equilibrium gel filtration. It is also adsorbed on nitrocellulose disks. Dissociation constant of the complex determined by nitrocellulose filter assay is 5 × 10^?8M.     

Structure of apo- and monometalated forms of NDM-1--a highly potent carbapenem-hydrolyzing metallo-β-lactamase

The New Delhi Metallo-β-lactamase (NDM-1) gene makes multiple pathogenic microorganisms resistant to all known β-lactam antibiotics. The rapid emergence of NDM-1 has been linked to mobile plasmids that move between different strains resulting in world-wide dissemination. Biochemical studies revealed that NDM-1 is capable of efficiently hydrolyzing a wide range of β-lactams, including many carbapenems considered as "last resort" antibiotics. The crystal structures of metal-free apo- and monozinc forms of NDM-1 presented here revealed an enlarged and flexible active site of class B1 metallo-β-lactamase. This site is capable of accommodating many β-lactam substrates by having many of the catalytic residues on flexible loops, which explains the observed extended spectrum activity of this zinc dependent β-lactamase. Indeed, five loops contribute "keg" residues in the active site including side chains involved in metal binding. Loop 1 in particular, shows conformational flexibility, apparently related to the acceptance and positioning of substrates for cleavage by a zinc-activated water molecule.     

Clumping factor A-mediated virulence during Staphylococcus aureus infection is retained despite fibrinogen depletion

Clumping factor A (ClfA), a fibrinogen-binding protein expressed on the Staphylococcus aureus cell surface, has previously been shown to act as a virulence factor in experimental septic arthritis. Although the interaction between ClfA and fibrinogen is assumed to be of importance for the virulence of S. aureus, this has not been demonstrated in any in vivo model of infection. Therefore, the objective of this study was to investigate the contribution of this interaction to ClfA-mediated virulence in murine S. aureus-induced arthritis. Ancrod, a serine protease with thrombin-like activity, was used to induce in vivo depletion of fibrinogen in mice. Ancrod treatment significantly aggravated septic arthritis following inoculation with a ClfA-expressing strain (Newman) compared to control treatment. Also, ancrod treatment tended to enhance the arthritis induced by a clfA mutant strain (DU5876), indicating that fibrinogen depletion exacerbates septic arthritis in a ClfA-independent manner. Most importantly, the ClfA-expressing strain was much more arthritogenic than the isogenic clfA mutant, following inoculation of fibrinogen-depleted mice. This finding indicates that the interaction between ClfA and free fibrinogen is not required for ClfA-mediated functions contributing to S. aureus virulence. It is conceivable that ClfA contributes to the virulence of S. aureus through interactions with other host ligands than fibrinogen.