muramidase and zinc-chloride

Lysozyme represents the best characterized enzyme involved in the self-defense from bacteria. In this study we analysed the effects of zinc on the lysozyme-like activity of the seastar Marthasterias glacialis mucus. This activity, detected by measuring the cleared lysis area of dried Micrococcus lysodeikticus cell walls on Petri dishes, was significantly reduced in presence of zinc. The results are discussed in the light of elucidating the possible relationship between environmental contaminants and increased disease susceptibility in seastars due to the decrease of antibacterial protection. The benefits of using the test of lysozyme activity to monitoring environmental pollution are highlighted.

Topics: Animals; Chlorides; Echinodermata; Environmental Pollutants; Mucus; Muramidase; Zinc Compounds

The function of autophosphorylation in Src family protein tyrosine kinases is not fully understood. In this paper we compared the catalytic and ligand-binding properties of autophosphorylated and nonautophosphorylated (control) Src. The following are the main differences we found. First, while both forms had the same K(m) for ATP-Mg, autophosphorylated Src had significantly higher K(m) values for the phosphate-accepting substrates, polyE(4)Y, and RCM-lysozyme. The autophosphorylated form also had significantly higher V(max) values than the control. The substrate specificity, as measured by V(max)/K(m) ratio, was altered by autophosphorylation and was dependent on the phosphate-accepting substrate. Second, while autophosphorylation did not affect Src activation by free Mg(2+), Zn(2+), which inhibited Src by competing against an essential Mg(2+) activator, inhibited the control threefold more potently than the autophosphorylated form. Third, autophosphorylation significantly reduced the ability of its SH2 domain to bind phosphotyrosine. Fourth, a Pro-rich Src SH3 domain binding peptide activated the control, but not the autophosphorylated Src even though the apparent binding affinity was not significantly affected by autophosphorylation. These differences indicated that autophosphorylation induced significant and widespread changes in the catalytic and regulatory properties of Src. The implications of these findings relative to Src biological regulation are discussed.

Topics: Catalysis; Chlorides; CSK Tyrosine-Protein Kinase; Dose-Response Relationship, Drug; Inhibitory Concentration 50; Kinetics; Ligands; Magnesium; Muramidase; Peptides; Phosphorylation; Phosphotyrosine; Protein Binding; Protein Structure, Tertiary; Protein-Tyrosine Kinases; Recombinant Proteins; Sepharose; Sodium Chloride; src Homology Domains; src-Family Kinases; Time Factors; Zinc; Zinc Compounds

Zinc is a physiological constituent of many human enzymes and also involved in an optimal immune response. Zinc deficiency as well as excessive zinc supplementation lead to disturbed functions of immune cells. In this study with isolated human polymorphonuclear leukocytes the toxic oxygen species generated during the oxidative metabolism were enhanced in presence of zinc ions. However, when the generation of superoxide anion was measured alone it was decreased by zinc. The phagocytic capacity was diminished in presence of zinc ions, too. The release of lysosomal enzymes was not influenced (lysozyme) or weakly inhibited (beta-glucuronidase). Our results may indicate an impairment of the microbicidal capacity due to the diminished phagocytosis, but a promotion of inflammatory reactions due to an increase of toxic oxygen species in the presence of zinc ions.

Topics: Acridines; Chlorides; Glucuronidase; Humans; Luminescent Measurements; Luminol; Muramidase; Neutrophils; Oxidation-Reduction; Oxygen; Phagocytosis; Superoxides; Zinc; Zinc Compounds