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At least 667 records · Page 37Linked to original sources
PubMed1984

A phenylalanine for serine substitution in the beta subunit of Escherichia coli F1-ATPase affects dependence of its activity on divalent cations.

A mutant (KF11) of Escherichia coli H+-translocating ATPase (F1-F0) has a single point mutation in the beta subunit of F1 that has lost 90% of its Mg2+-dependent ATPase activity (Kanazawa, H., Horiuchi, Y., Takagi, M., Ishino, Y., and Futai, M. (1980) J. Biochem. (Tokyo) 88, 695-703). The mutation was mapped at about the 500th nucleotide residue from the 5' end of the beta subunit gene by a genetic recombination test on the physical map of the cistron coding for the beta subunit. The mutant allele of KF11 (uncD11) was cloned on a hybrid plasmid (pKF11) via DNA isolated from a lambda uncD11 transducing phage. Restriction fragments of pKF11 containing the estimated mutation site were subjected to polyacrylamide gel electrophoresis under conditions where strands were separated into single strands. The two strands of a DNA segment, which was shown to carry an altered base, showed anomalous migration compared with those from the wild-type fragment. The results confirmed the result of mapping of the altered site by genetic tests. On the basis of these results, the nucleotide sequence of the mutated gene was determined, and a single base change of the 524th cytosine to thymine resulting in a phenylalanine for serine substitution at residue 174 of the beta subunit was found. This result, together with results on the altered properties of F1 from KF11 reported previously, indicates that residue 174 is essential for the Mg2+-dependent ATPase activity of F1 but not for the Ca2+-dependent ATPase activity.

Amino Acid Sequence↗
PubMed1982

[Effect of divalent cations on the properties of NaCl-stimulated ATPase activity in the mucosa of the rabbit small intestine].

The effect of bivalent cations on NaCl-stimulated ATPase activity in rabbit small intestinal mucosa was studied. Unlike Ba2+ and Zn2+, Ca2+ and Mg2+ added to the incubation medium at a concentration of 0.25 mM completely change ATPase activity. Histamine considerably reduces the inhibitory effect of Ca2+ and Mg2+ on NaCl-stimulated and oligomycin-inhibited ATPase activity. Possible mechanisms of the enzyme activity control in the cell are discussed.

Adenosine Triphosphatases↗
PubMed1983

Calcium alters divalent cation modulation of brain benzodiazepine receptors.

Nickel (Ni+2) ions enhance the binding of 3H-diazepam, but decrease the binding of 3H-propyl beta-carboline-3-carboxylate to benzodiazepine receptors in mouse brain. Our experiments were performed to determine the locus for this action. In both control and Ca+2-depleted membranes, Ca+2 blocked the stimulatory effect of Ni+2 on 3H-diazepam binding in a concentration-dependent manner. In Ca+2-depleted membranes, physiological Ca+2 concentrations blocked this effect of Ni+2. In control membranes, Ca+2 did not reverse Ni+2 inhibition of 3H-propyl beta-carboline-3-carboxylate binding, but was effective at physiological concentrations in reversing Ni+2 inhibition in Ca+2-depleted membranes. The effects of Cd+2 ions on 3H-diazepam binding were similar to Ni+2 and were also reversed by Ca+2. The effects of Ni+2 were blocked by La+3 ions but not by Mg+2 ions, and were not due to interactions with the GABA receptor or Cl- ionophore. These data suggest that a Ca+2 binding site is associated with the brain benzodiazepine receptor.

Animals↗
PubMed1983

[Changes in the structure of the chromosomal nucleohistone fibrils on removal of divalent cations and histone H1].

A technique of freeze--drying was applied in studies on submicroscopic organization of metaphase chromosomes from Chinese hamster. In the buffer without bivalent cations the chromosomes increased in size; the removal of bivalent cations with EDTA resulted in a large swelling of chromosomes. Regularly organized nucleosomal filaments of a "beads-on-a-string" type appeared on the periphery of chromosomes. The regular organization of the fibers is damaged as soon as histone H1 is removed. An increase in the ionic strength of solution in the absence of bivalent cations results in chromosome compactization, although the regular fibrillar structure being not restored.

Animals↗
PubMed1981

[Action of divalent cations on the mechanoreceptor of isolated frog heart (author's transl)].

Afferent activities were recorded in vagosympathetic nerves from mechanoreceptors of the isolated heart of bullfrog. The rate of discharges was increased when Ca2+ or Mg2+ (1.1 approximately 4.4 mM) was added to normal Ringer's solution containing 1.1 mM Ca2+. In terms of increase in the rate of discharges following the addition of Ca2+, an increase in the tone of cardiac muscle at diastole was observed. The rate of discharges was decreased and thereafter abolished within 5 to 10 min by lowering Ringer's solution Ca2+ concentration from 1.1 to 0.37 mM. A high firing frequency was observed with the addition of Mg2+ (0.73 mM) in the low Ca2+ Ringer's solution containing 0.37 mM Ca2+ and the rate remained unchanged for at least 15 min. On the other hand, the discharges were reduced, concentration dependently, when Mn2+ (0.22 approximately 1.1 mM) was added to normal Ringer's solution. When Mn2+ (0.22 or 0.55 mM) was applied, the rate of discharges decreased gradually and the reduction of discharges decreased 10 to 20 min after application. It appears that increase in the rate of discharges by application of Ca2+ is mainly the result of an increase in the tone of cardiac muscle induced by Ca2+. The presence of Ca2+ in external medium seems to be necessary to maintain the generation afferent discharges and Mg2+ can act as a substitute for Ca2+ in the generation of afferent discharges. The inhibitory effect of Mn2+ seems to be the result of depression of mechanoreceptors but the receptor becomes insensitive to Mn2+ within 10 to 20 min during exposure to low concentrations of Mn2+.

Action Potentials↗
PubMed1982

Regulation of parathyroid hormone secretion in vitro by divalent cations and cellular metabolism.

Parathyroid hormone (PTH) secretion was investigated in intact cells isolated in vitro. Parathyroid cells from bovine parathyroid glands were obtained through tissue dispersion and cell purification through isotonic Percoll gradients, a newly developed protocol enhancing cell homogeneity and viability. Isolated cells maintained both metabolic viability and plasma membrane intactness for over 3 h at 37 degrees C, as shown by the large ATP/ADP ratios and the high intracellular K+ content (ouabain-sensitive) measured. The rate of PTH secretion was inversely related to the Ca2+ concentrations in the medium; secretion was 54 and 18 ng PTH/mg of protein/min when free Ca2+ in the buffer was 0.8 and 2 mM, respectively. At either Ca2+ concentration, PTH secretion was strongly dependent on cell metabolism; it was inhibited by 80-85% within 10 min when cells were suspended in glucose-free buffer containing either cyanide or oxidative phosphorylation uncoupler. Under these conditions, both cellular ATP production and calcium-dependent PTH release could be partially restored by addition of 5 mM glucose. La3+, Mn2+, Sr2+, Ba2+, and Mg2+ were each tested in a range of 0.5-2.5 mM for their effects in suppressing low calcium-stimulated secretion. La3+ and Mn2+ were about twice as effective as Ca2+ on a molar basis, Sr2+ was similar to Ca2+, Mg2+ was about half as effective, and Ba2+ had almost no effect. These results suggest that the Ca2+-dependent stimulus-secretion coupling of these cells is largely different from that established in other secretory cells and provide an in vitro system to further investigate the regulation of PTH secretion.

Adenosine Diphosphate↗