Distribution Of Adenine Nucleotides Research Articles

The Influence of Hypoxia and Anoxia on Distribution of Adenine Nucleotides in Isolated Hepatocytes

Isolated hepatocytes incubated under conditions of "chemical hypoxia" (KCN + iodoacetic acid) exhibited a marked dephosphorylation of the cytoplasmic and mitochondrial adenine nucleotides to AMP. Cytoplasmic adenine nucleotide levels (ATP + ADP + AMP) were decreased by 40%. There was no significant change in the mitochondrial adenine nucleotide pool size. For starved rats, but not for fed rats, addition of KCN to isolated hepatocytes resulted in a shift of the mitochondrial adenine nucleotide species to AMP. This difference was correlated with the maintenance of a substantial level of cytoplasmic ATP in the fed vs starved condition. The addition of fructose (but not glucose) to hepatocytes isolated from a starved rat, prevented the KCN-induced dephosphorylation of mitochondrial adenine nucleotides to AMP. Fructose-treated cells had a significant level of ATP in the cytoplasm, whereas glucose-treated cells did not. Addition of A23187 to fructose-treated (but not glucose-treated) cells resulted in a net loss in the mitochondrial adenine nucleotide content. The results suggest that the shift of matrix adenine nucleotides from ATP and ADP to AMP preserves the mitochondrial adenine nucleotide pool size during transient hypoxia by preventing net adenine nucleotide transport to the cytoplasm via the ATP-Mg/Pi carrier. This effectively protects those adenine nucleotides from the cytoplasmic purine degradation pathway, a strategy that has the potential to facilitate rapid recovery of bioenergetic status by oxidative phosphorylation upon reoxygenation.

Long-term and short-term changes in mitochondrial parameters by thyroid hormones.

In the hyperthyroid state, delta psi m, delta pHm and therefore delta p are increased in rat liver. An enhanced delta p accords with a higher energy output. The subcellular distribution of adenine nucleotides in different thyroid states does not reflect the driving force for mitochondrial adenine-nucleotide translocase (that is delta psi m). Therefore, a change in delta psi m cannot be solely responsible for the postulated stimulation of adenine-nucleotide transport by THs. This is also the case for the changes in delta pHm, and in the subcellular distribution of malate, 2-oxoglutarate and glutamate, that are observed under the influence of THs. T3 induces calcium influx into the liver cell within minutes. It increases respiration and gluconeogenesis with the same kinetics. Therefore, it is suggested that, as with glucagon and vasopressin, calcium is the mediator of these changes. The delta p is increased with T3 and glucagon treatment but not with vasopressin. The changes in delta psi m and delta pHm appear to be the result of the individual actions of these hormones on ATP-consuming and ATP-producing reactions. The delta psi p is only increased with T3 treatment. This is related to the different mechanisms of enhancing intracellular calcium that are used by vasopressin, glucagon and T3.

The Na+K+-ATPase inhibitor ouabain reduces the effect of the K+-ionophore Valinomycin on adenine nucleotide distribution

The Na+K+-ATPase inhibitor ouabain reduces the effect of the K+-ionophore Valinomycin on adenine nucleotide distribution

Subcellular Distribution of Adenine Nucleotides in Two Ehrlich Cell Lines Metabolizing Glucose

Adenine nucleotide compartmentation and cytochrome redox state were studied in two Ehrlich ascites tumor cell lines incubated in the presence of 5mM glucose to show differences between their energy metabolisms. Changes in the subcellular distribution of adenine nucleotides were very different in both cell lines. Glucose seemed to energize the less malignant cell line, as shown by the asymmetry of the ATP/ADP ratios between cytosolic and mitochondrial compartments, but this was not the case for the more malignant cell line. The cytochrome contents were similar in both cell lines, but the degree of cytochrome oxidation was higher in the less malignant cell line; this result is in agreement with a higher oxygen consumption in the less malignant cell line.

Computer Simulation of the Fructose Bisphosphatase/Phosphofructokinase Couple in Rat Liver

Recycling of fructose 6-phosphate and fructose 1,6-bisphosphate in the rat liver under gluconeogenic and glycolytic conditions was investigated with a computer model containing representations of the kinetic properties of phosphofructokinase and fructose 1,6-bisphosphatase under realistic physiological conditions. The two enzyme submodels were constructed from data for the isolated enzymes in vitro by formal optimization. Tissue metabolite concentrations were corrected for cytosolic/mitochondrial compartmentation and effects of chelation and protonation equilibria. This model, which mostly considers the behavior of livers from starved rats, predicts negligible recycling under physiologically realistic conditions. Metabolic regulation of fructose 6-phosphate, the magnesium ion concentration and the distribution of adenine nucleotides appear to prevent operation of a 'futile cycle' in vivo. Rate-limiting chemical species were identified by sensitivity analysis.

Distribution of adenine nucleotides between the inner and outer spaces of the mitochondrion as a determinant of phosphorylation pattern.

Mitochondrial preparations incubated with 32P1 and 3H-ADP were subjected to rapid filtration through a Millipore filter to study the intramitochondrial distribution of labelled nucleotides. The atractyloside-induced inhibition of the distribution of internally-labelled nucleotides and of externally-added 3H-ADP revealed that the nucleotides in the matrix space are successfully separated by this means from those outside the inner membrane. The addition of Mg2+ to the incubation medium has no effect on the labelling pattern in the matrix space but results in a rapid interconversion of adenine nucleotides outside the inner membrane through the activation of adenylate kinase [EC 2.7.4.3] and nucleosidediphosphate kinase [EC 2.7.4.6], which do not function in an Mg2+-free medium. The localization of GTP-AMP phosphotransferase [EC 2.7.4.10] outside the membrane is questionable, but was not definitely excluded. The translocation of internal ATP outwards in exchange for external ATP or ADP induced by the addition of ATP or ADP, of hexokinase plus glucose or of myokinase (muscle adenylate kinase) plus AMP into the incubation medium appears to be a significant factor in promoting the labelling of ATP, reflecting oxidative phosphorylation. 32P1-Labelling of ADP dependent on substrate-level phosphorylation is greatly suppressed under these conditions. This apparent suppression of substrate-level phosphorylation is at least partly accounted for in terms of the lowered specific radioactivity of the P1 compartment selectively supporting AMP phosphorylation as compared to the specific radioactivity of the major P1 pool serving as the substrate for oxidative phosphorylation. A possible interaction of these two phosphorylation reactions in rat-liver mitochondria is also discussed.

Effects of ischemia on the concentration of adenine nucleotides in the kidney of anesthetized dogs.

SummaryIschemia causes a rapid decline in the concentration of ATP in the kidney cortex of anesthetized dogs. Within 8 sec of ischemia distribution of adenine nucleotides is determined by activity of adenylate kinase. Nucleotide metabolism of the cortex of dog is distinguished from that of rat by the observation that concentrations are lower and by the evidence of activity of adenylate kinase. We estimate that blood-flow dependent ATP turnover in the cortex is 27% of that calculated on the basis of renal O2 consumption. The medulla, in contrast to the cortex, maintains its ATP concentration during 60 sec of interruption of blood flow. Studies of nucleotide metabolism in the kidney must include consideration of differences in adenylate kinase activity between cortex and medulla and between different mammalian species.