Production of cholinesterase by Pseudomonas aeruginosa, its regulation by glucose and cyclic AMP and inhibition by antiserum

Production of cholinesterase by a pyocyanin-producing strain of Pseudomonas aeruginosa, isolated from a patient and grown in the presence of acetylcholine as the main source of carbon, was described. The enzyme activity was detected in suspensions of intact bacteria and in their subcellular preparations. Like the acetylcholinesterase of the electric eel, as opposed to that of the erythrocytes, this bacterial enzyme was inhibited by specific antiserum produced against it in rabbits. The production of the enzyme was found to be sensitive to catabolite repression and to require external cyclic AMP, but not 5′-AMP for the elimination of this repression. Cyclic AMP alone, without the inducer, did not stimulate the production of the enzyme.     

Tiron as a spin-trap for superoxide radicals produced by the respiratory chain of submitochondrial particles

Tiron can be used as a spin-trap for O2 radicals generated by the respiratory chain of submitochondrial particles (SMP). Using this sensitive method, it was shown that the O2 (radical) production by the succinate-oxidizing SMP can be reduced by antimycin or 4-nonyl-2-hydroxyquinoline-N-oxide, the effects of both antibiotics being abolished and prevented by cyanide. It is suggested tht the O2 radicals are produced due to autooxidation of ubisemiquinone which is formed as an intermediate upon one-electron oxidation of CoQH2 by cytochrome c1. The effects of antimycin, 2-nonyl-4-hydroxyquinoline-N-oxide and cyanide on the O2 (radical) generation correlate with the effects of these inhibitors on a steady-state concentration of ubisemiquinone predicted by the Mitchell's Q-cycle hypothesis.     

Role of Asp-9 and Glu-36 in the active site of the pneumococcal CPL1 lysozyme: an evolutionary perspective of lysozyme mechanism.

The role of carboxylic amino acids Asp-9 and Glu-36 in the activity of CPL1 lysozyme was investigated by site-directed mutagenesis. The enzymatic activity of the single mutants D9E, D9N, D9H, D9K, D9A, E36D, E36Q, E36K, and E36A and of the double mutant D9A-E36A was analyzed using a highly sensitive radioactive assay. All mutants but D6K showed detectable activities. Interestingly, the mutants E36D and E36Q retained 67% and 37% activity, respectively. Amino acid replacements at position 9 turned out to be more critical for activity than at position 36. In analogy to the mechanism described for hen egg-white lysozyme, where the proton donor play a central role, we propose that, in the CPL1 lysozyme, Asp-9 might act as the proton donor for activation of the substrate, and Glu-36 could help in the stabilization of the intermediate oxocarbocation. The residual activity of lysozyme mutants lacking one or two of the acidic amino acids may be explained by the participation of a water molecule as proton donor and/or to electrostatic contributions in the active center stabilizing the transition state of the reaction. Our results are in agreement with the hypothesis that enzymes have been optimized during evolution from an ancestral protein able to bind more tightly the transition state of the substrate than the substrate itself, by the acquisition of amino acids serving a function in catalysis.     

Phosphorylation by cAMP-dependent protein kinase inhibits the degradation of tau by calpain.

The effects of cAMP-dependent protein kinase (cAMP-PK) phosphorylation on the degradation of the microtubule-associated protein tau by calpain were studied. Purified bovine brain tau that had been phosphorylated by cAMP-PK had a slower migration pattern on sodium dodecyl sulfate-polyacrylamide gels and a more acidic, less heterogeneous pattern on two-dimensional, nonequilibrium pH gradient electrophoresis (NEPHGE) gels compared with untreated tau. Phosphorylation of tau by cAMP-PK significantly inhibited its proteolysis by calpain compared with untreated tau. To our knowledge this is the first demonstration that phosphorylation of tau by a specific kinase results in increased resistance to hydrolysis by calpain. Tau dephosphorylated by alkaline phosphatase migrated more rapidly on sodium dodecyl sulfate-polyacrylamide gels and also showed an altered two-dimensional NEPHGE pattern. Dephosphorylation of tau had no effect on its susceptibility to calpain proteolysis, indicating that regulation of the susceptibility to calpain hydrolysis is due to the phosphorylation of a specific site(s). These results suggest a role for phosphorylation in regulating the degradation of tau. Abnormal phosphorylation could result in a protease-resistant tau population which may contribute to the formation of paired helical filaments in Alzheimer's disease.