scholarly journals Sub-micromolar concentrations of extramitochondrial Ca2+ stimulate the rate of citrulline synthesis by rat liver mitochondria

1989 ◽  
Vol 257 (1) ◽  
pp. 285-288 ◽  
Author(s):  
J D Johnston ◽  
M D Brand
Keyword(s):  
Rat Liver ◽  
Urea Cycle ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Hormonal Stimulation ◽  
Isolated Rat Liver ◽  
Citrulline Synthesis ◽  
Isolated Rat ◽  
Stimulation Of

1. In the presence of physiological concentrations of Na+ and Mg2+, the rate of citrulline synthesis by isolated rat liver mitochondria respiring on a range of substrates was stimulated by up to 60% when the extramitochondrial Ca2+ concentration was raised from 130 pM to 770 nM. 2. Our findings suggest that hormonal stimulation of the urea cycle may be mediated by Ca2+.

scholarly journals Regulation of glycine catabolism in rat liver mitochondria

1992 ◽  
Vol 283 (2) ◽  
pp. 435-439 ◽  
Author(s):  
M Jois ◽  
H S Ewart ◽  
J T Brosnan
Keyword(s):  
Rat Liver ◽  
Fold Increase ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Mitochondrial Matrix ◽  
Isolated Rat Liver ◽  
Matrix Volume ◽  
Isolated Rat ◽  
Stimulation Of

1. The catabolism of glycine was studied in isolated rat liver mitochondria by measuring release of 14CO2 from [1-14C]-glycine. Incubation of mitochondria in a medium containing 0.5 microM free Ca2+ resulted in an 8-fold increase in the rate of degradation of glycine. Intraperitoneal injection of glucagon (33 or 100 micrograms/100 g body wt.) 25 min before killing of rats also resulted in a 3-fold or 10-fold (depending on dosage) increase in the rate of catabolism of glycine. 2. Both the stimulation by free Ca2+ and that by injection of glucagon in vivo were dependent on phosphate in the incubation medium. This requirement for phosphate was specific, as replacement of phosphate by other permeant anions such as thiocyanate and acetate did not permit the stimulation. The phosphate-dependent stimulation of glycine catabolism by Ca2+ was also evident when mitochondria were incubated in the absence of K+. 3. Mitochondria isolated from rats previously injected with glucagon showed elevated rates of degradation of glycine even in the presence of rotenone, provided that regeneration of NAD+ was affected by providing acetoacetate. 4. Hypo-osmolarity of the medium markedly stimulated the rate of degradation of glycine by mitochondria. Although hypo-osmolarity-induced stimulation of glycine degradation was accompanied by parallel changes in mitochondrial matrix volume, no measurable changes in matrix volume were observed in mitochondria stimulated either by free Ca2+ (0.5 microM) or by injection of glucagon in vivo. Furthermore, Ca2+ stimulated glycine decarboxylation in mitochondria exposed to either hyper-osmolar (410 mosmol) or hypo-osmolar (210 mosmol) conditions. Although hyper-osmolarity decreased and hypo-osmolarity increased matrix volume, stimulation of glycine degradation by Ca2+ was not associated with any further changes in matrix volume. 5. These data demonstrate that the regulation of hepatic glycine oxidation by glucagon and by free Ca2+ is largely independent of changes in mitochondrial matrix volume.

Quantification of the control exerted by different steps during citrulline synthesis in isolated rat liver mitochondria

1983 ◽  
Vol 11 (1) ◽  
pp. 89-90 ◽  
Author(s):  
RONALD J. A. WANDERS ◽  
ALFRED J. MEIJER ◽  
CARLO M. VAN ROERMUND ◽  
ALBERT K. GROEN ◽  
COR LOF ◽  
...  
Keyword(s):  
Rat Liver ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Isolated Rat Liver ◽  
Citrulline Synthesis ◽  
Isolated Rat

scholarly journals The stimulation of glutamine hydrolysis in isolated rat liver mitochondria by Mg2+ depletion and hypo-osmotic incubation conditions

1981 ◽  
Vol 194 (1) ◽  
pp. 35-41 ◽  
Author(s):  
S K Joseph ◽  
J D McGivan ◽  
A J Meijer
Keyword(s):  
Rat Liver ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Ionophore A23187 ◽  
Inner Membrane ◽  
Isolated Rat Liver ◽  
Low Concentrations ◽  
Glutaminase Activity ◽  
Isolated Rat ◽  
Stimulation Of

1. In respiring rat liver mitochondria EDTA stimulates glutaminase activity measured in the presence of phosphate and HCO3- ions. The stimulation can be reversed by the addition of low concentrations of MgCl2. EGTA does not stimulate glutamine hydrolysis. 2. Glutaminase activity assayed in disrupted mitochondria is not significantly affected by EDTA or MgCl2. 3. The addition of EDTA results in a decrease in the concentration of phosphate required for half-maximal glutaminase activity. 4. Depletion of mitochondrial Mg2+ by the addition of the ionophore A23187 also stimulates glutamine hydrolysis in both the presence and the absence of EDTA. The effect of the ionophore can be abolished by the addition of MgCl2. 5. Hypo-osmotic incubation conditions increase the rate of mitochondrial glutamine hydrolysis. The effect of hypo-osmoticity on glutaminase is much less when EDTA is present. 6. It is suggested that glutaminase is partially and indirectly inhibited by endogenous mitochondrial Mg2+ and that the inner membrane may play a role in the regulation of glutaminase activity.

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