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At least 397 records · Page 22Linked to original sources
PubMed1982

Different classes of nucleotide binding sites in the (Na+ + K+)-ATPase studied by affinity labeling and nucleotide-dependent SH-group modifications.

The ATP analog 6-[(3-carboxy-4-nitrophenyl)thiol]-9-beta-D-ribofuranosylpurine 5'-triphosphate (Nbs6ITP) is slowly hydrolyzed at pH 7.4 by the (Na+ + K+)-ATPase, whereas it binds covalently at pH 8.5 and inhibits the enzyme irreversibly. Time courses of irreversible inhibition could only be fitted to a model in which the enzyme can exist in two slowly interchangeable states, one of which is enzymatically active and binds Nbs6ITP first reversibly and then covalently. Arguments that the covalent binding occurs at a low affinity nucleotide binding site are: (a) similarity of the Ki Nbs6ITP for the reversible and the irreversible inhibition and of K0.5 for ATP protection; (b) stoichiometry of covalent Nbs6ITP binding per alpha subunit of 0.8; and (c) change of complex substrate dependence of the enzyme to a Michaelis-Menten type after Nbs6ITP modification. This change in kinetics and the finding that the Nbs6ITP inactivation at a low affinity nucleotide binding site is increased by micromolar ADP concentrations indicates that the (Na+ + K+)-ATPase contains two different nucleotide binding sites. Since studies of nucleotide effects on enzyme inactivation by 5,5'-dithiobis(2-nitrobenzoic acid) did not confirm the hypothesis of an SH-group in a nucleotide binding site, Nbs6ITP may bind to another functional group, e.g. to an OH-group of tyrosine.

Adenosine Triphosphate↗
PubMed1984

Polymorphonuclear leukocytic inhibition by citrate, other metal chelators, and trifluoperazine. Evidence to support calcium binding protein involvement.

Corneal ulceration after severe alkali burns of the eye is thought to result principally from collagen breakdown as a consequence of local polymorphonuclear leukocyte (PMN) activities. The favorable effect of topical citrate on such burns suggested a direct effect on these inflammatory cells. These in vitro studies show that the stimulation of human PMN by opsonized zymosan can be inhibited by citrate, EDTA, and EGTA. These compounds interfere with opsonized zymosan attachment to PMN, preventing the respiratory burst, phagocytosis, and degranulation. Reversal of this inhibition by calcium and/or magnesium suggests that mechanism is calcium chelation. Trifluoperazine (TFP) inhibition of opsonized zymosan attachment and phagocytosis implicates the involvement of calmodulin. We propose that citrate, EDTA, and EGTA interfere with the receptor mediated attachment of opsonized zymosan to the PMN cell membrane, leaving the PMN in a resting, granulated state. Inhibition of the receptor system by calcium depletion may be the result of interference with calcium-calmodulin modulated microfilament and/or microtubule interfaces in the PMN plasma membrane. It is postulated that comparable events occur in the citrate treated alkali burned cornea. Citrate inhibition of PMN may be useful in other eye and systemic diseases.

Burns↗
PubMed1980

The dispersion of gram-negative lipopolysaccharide by deoxycholate. Subunit molecular weight.

The lipopolysaccharide (LPS) was isolated from three strains of Salmonella typhimurium, a "smooth" strain, STM 7, the Ra mutant, TV 119, and the Re mutant, SL 1102. The effect of depletion of divalent cations on structure and the effect of deoxycholate on hydrodynamic behavior were studied. The results confirmed previous work by others that divalent cations and hydrophobic forces are important factors influencing LPS size and morphology. The binding of deoxycholate to LPS was measured. When the weight average molecular weights of the deoxycholate-dissociated LPS were determined by sedimentation equilibrium and corrected for bound deoxycholate, the values 5,555, 10,607, and 15,592, respectively, for Re, Ra, and "smooth" LPS were in good agreement with calculated formula weights. Although others have suggested that the basic LPS subunit is a trimer, our results suggest that it exists in the dimeric form.

Binding Sites↗
PubMed1981

[Extracellular toxins of Pseudomonas aeruginosa. I. Purification and characterization of two exoproteases (author's transl)].

Alkaline protease (protease I) and a protease with elastase activity (protease II) were isolated from two different strains of Pseudomonas aeruginosa (PA). Proteolytic activity was measured during the early exponential phase of growth and was highest when cultures reached the stationary growth phase. The extracellular character of protease I and II was demonstrated by measuring the intra- and extracellular ATP-concentration. Purification was achieved by precipitation with 65% ammonium sulfate, precipitation with 70% acetone, gelfiltration on Sephadex G-100 and chromatography on DEAE-Sephacel. The purified proteases were characterized. The pH for optimal proteolytic activity of protease I was at pH 9--10, for protease II at pH 8--9. Both enzymes cleaved casein and gelatine, in addition protein II elastin. Enzymatic activity of protease II was inhibited by 10(-3) M EDTA at pH 8.1 to 82%. Inactivation of protease I was not achieved by 10(-2) M EDTA. Molecular weight of protease I was estimated at 57,000, molecular weight of protease II at 39,000. Both enzymes consist of one polypeptide chain. In isoelectric focusing the protease I was separated into two components with pH values of 8.5 and 8.7, while protease II had isoelectric points of pH 6.0 and 6.4. Further characterization of protease I was done with amino acid analysis. Protease I was fairly stable over a pH range of 6--9 at room temperature. The optimal temperature for proteolytic activity was 60 degrees C. The results are discussed in view of proteases of other PA-strains.

Amino Acids↗