We have previously shown that liver plasma membrane (Ca2+-Mg2+)-ATPase activity is inhibited by glucagon. To investigate the possible involvement of a GTP-binding (G) protein in this regulation, we have examined the effects of pertussis toxin and cholera toxin on inhibition of (Ca2+-Mg2+)-ATPase by glucagon. Treatment of liver plasma membranes with pertussis toxin did not affect the sensitivity...

Interactions with magnesium (Mg2+) ions are essential for RNA folding and function. The locations and function of bound Mg2+ ions are dif®cult to characterize both experimentally and computationally. In particular, the P456 domain of the Tetrahymena thermophila group I intron, and a 58 nt 23s rRNA from Escherichia coli have been important systems for studying the role of Mg2+ binding in RNA, bu...

Recently it has been suggested that Mg deficiency may play a key role in hypertension and several cardiovascular diseases. In order to investigate the status of Mg in genetic hypertension, the cytosolic free Mg2+ concentration ([Mg2+]i) in the lymphocytes and serum concentrations of free Mg2+ and total Mg were measured in spontaneously hypertensive rats/Izumo (SHR/Izm), stroke-prone spontaneous...

Extracellular Mg2+, which blocks NMDA channels in a voltage-dependent manner and increases the receptor's affinity for glycine, is shown here to potentiate NMDA responses at saturating glycine concentrations. This potentiation, induced by millimolar concentrations of Mg2+, is not mimicked by Ca2+ and Ba2+ and is voltage independent. The potentiation is variable in native receptors of cultured m...

The requirement for Ca2+ and Mg2+ in the actions of insulin and sodium nitroprusside on rat adipocyte metabolism was investigated: sodium nitroprusside, but not insulin, increased cGMP levels in cells incubated in the absence of Ca2+ and/or Mg2+; sodium nitroprusside and insulin are unable to increase the incorporation of [14C]glucose into triglycerides and [14C]leucine into proteins in the abs...

Studies of Escherichia coli membranes that were highly enriched in the Salmonella enterica serovar Typhimurium PhoQ protein showed that the presence of ATP and divalent cations such as Mg2+, Mn2+, Ca2+, or Ba2+ resulted in PhoQ autophosphorylation. However, when Mg2) or Mn2+ was present at concentrations higher than 0.1 mM, the kinetics of PhoQ autophosphorylation were strongly biphasic, with a...

Purified perigranular and plasma membranes isolated from rat peritoneal mast cells were examined for Ca2+- and Mg2+-dependent ATPase activity. Isolated perigranular membranes contained only a low-affinity Ca2+- or Mg2+-dependent ATPase (Km greater than 0.5 mM). The plasma membranes contained both a low-affinity Ca2+- or Mg2+-dependent ATPase (Km = 0.4 mM, Vmax. = 20 nmol of Pi/min per mg), as w...

A membrane fraction enriched in endoplasmic reticulum was prepared from rat parotid glands by using sucrose-gradient centrifugation. The fraction showed a 10-fold increase in specific activity of NADPH: cytochrome c reductase activity over that of tissue homogenates and minimal contamination with plasma membranes or mitochondria. The endoplasmic reticulum fraction possessed both Mg2+ -stimulate...

Membrane phosphorylation and nucleoside triphosphatase activity of sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle were studied using ATP and ITP as substrates. The Ca2+ concentration was varied over a range large enough to saturate either the high affinity Ca2+-binding site or both high and low affinity binding sites. In intact vesicles, which are able to accumulate Ca2+, ...

The effect of divalent cations on cation fluxes across the chloroplast envelope and on photo­ synthetic reactions of intact spinach chloroplasts was investigated. In the absence of EDTA, divalent cations inhibited photosynthetic C02-fixation and PGAreduction at low PGA concentrations, but had almost no effect on the reduction of OAA, BQ, and on PGA-reduction at high PGA concentrations. The inhi...