guanosine-triphosphate and Starvation

Topics: Adenosine Triphosphate; Bacillus subtilis; Cerulenin; Fatty Acid Synthesis Inhibitors; Fatty Acids; Guanosine Triphosphate; Ligases; Membrane Potentials; Starvation; Stress, Physiological

In the myocardium and skeletal muscles of rats deprived of food for 2 days, basal activity of adenylate cyclase decreased, while the sensitivity of adenylate cyclase signaling system to the stimulating effects of non-hormonal agents (guanine nucleotides and NaF) and beta-agonist isoproterinol modulating adenylate cyclase through stimulating G proteins increased. In starving organism, the regulatory effects of hormones realizing their effects through inhibitory G proteins (somatostatin in the myocardium and bromocryptin in the brain) weakened. Their inhibitory effects on forskolin-stimulated adenylate cyclase activity and stimulating effects on binding of guanosine triphosphate decreased. In the brain of starving rats, the differences in the sensitivity of the adenylate cyclase signaling system to hormones and nonhormonal agents were less pronounced than in the muscle tissues, which attested to tissue-specific changes in the functional state of this system under conditions of 2-day starvation.

Topics: Adenylyl Cyclases; Animals; Biogenic Amines; Brain; Bromocriptine; Colforsin; Guanosine Triphosphate; Heart; Isoproterenol; Male; Muscle, Skeletal; Myocardium; Rats; Rats, Wistar; Serotonin; Signal Transduction; Somatostatin; Starvation

In rats, 48-h starvation causes a decrease in the rate of protein synthesis in skeletal (e.g. gastrocnemius) muscle, due largely to impairment of peptide-chain initiation. In other cell types inhibition of initiation is associated with decreased activity and recycling of initiation factor eIF-2, and increased phosphorylation of its alpha-subunit. However, 48-h starvation has no effect on the activity or recycling of eIF-2 measured in extracts of gastrocnemius muscle, or on the level of alpha-subunit phosphorylation. The effects of starvation on peptide-chain initiation in skeletal muscle must therefore involve alterations in other components of the translational machinery.

Topics: Animals; Eukaryotic Initiation Factor-2; Guanosine Diphosphate; Guanosine Triphosphate; Kinetics; Male; Muscles; Peptide Initiation Factors; Phosphorylation; Polyribosomes; Proteins; Rats; Rats, Inbred Strains; Reference Values; Ribosomes; RNA, Transfer, Met; Starvation

Starvation, diabetes and insulin did not alter the concentration of casein kinases in rat liver cytosol. However, the Km for casein of casein kinase 2 from diabetic rats was about 2-fold lower than that from control animals. Administration of insulin to control rats did not alter this parameter, but increased the Km for casein of casein kinase 2 in diabetic rats. Starvation did not affect the kinetic constants of casein kinases. The effect of diabetes on casein kinase 2 persisted after partial purification of the enzyme by glycerol-density-gradient centrifugation and affected also its activity on other protein substrates such as phosvitin, high-mobility-group protein 14 and glycogen synthase. The results indicate that rat liver cytosol casein kinase 2 is under physiological control.

Topics: Animals; Casein Kinases; Cytosol; Diabetes Mellitus, Experimental; Guanosine Triphosphate; Insulin; Isoenzymes; Kinetics; Liver; Male; Protein Kinases; Proteins; Rats; Rats, Inbred Strains; Starvation; Substrate Specificity

Topics: Adenylyl Cyclases; Adipose Tissue; Catecholamines; Guanosine Monophosphate; Guanosine Triphosphate; Humans; Propranolol; Starvation

The effect of cold exposure (5 degrees C) on the concentration of cyclic AMP and on the activity of phosphoenolpyruvate carboxykinase (GTP: oxaloacetate carboxy-lyase (transphosphorylating), EC 4.1.1.32) was investigated in the liver of intact and adrenalectomized starved rats. Intact starved rats responded to cold exposure with a large increase in both the concentration of hepatic cyclic AMP and the activity of phosphoenolpyruvate carboxykinase above the starvation level. Adrenalectomy did not impair the cold-induced maximum elevation of cyclic AMP but totally prevented the response of the enzyme to cold. Yet, this response was completely restored by hydrocortisone treatment, while the steroid per se had no effect on enzyme activity. In isolated perfused livers of intact starved rats dibutyryl cyclic AMP provoked an immediate dramatic increase in phosphoenolpyruvate carboxykinase activity above the starvation level even if mRNA synthesis was inhibited by cordycepin. However, cyclic AMP was ineffective in increasing enzyme activity in livers of adrenalectomized rats. From these results it is suggested (i) that in starved rats the adaptation to the enhanced glucose demand provoked by cold exposure includes the induction of hepatic phosphoenolpyruvate carboxykinase above the starvation level, (ii) that this induction is due to the cold-induced increase in hepatic cyclic AMP levels, (iii) that cyclic AMP stimulates enzyme synthesis at a post-transcriptional step and (iv) that the cold-induced cyclic AMP-mediated induction of phosphoenolpyruvate carboxykinase above the starvation level requires the "permissive" effect of glucocorticoids.

Topics: Adrenalectomy; Animals; Blood Glucose; Bucladesine; Cold Temperature; Cyclic AMP; Deoxyadenosines; Guanosine Triphosphate; Hydroxycorticosteroids; Insulin; Liver; Male; Phosphoenolpyruvate Carboxykinase (GTP); Rats; Starvation

Topics: Animals; Aurintricarboxylic Acid; Creatine Kinase; Guanine Nucleotides; Guanosine Triphosphate; Kinetics; Magnesium; Methionine; Muscles; Myocardium; Organ Specificity; Peptide Initiation Factors; Phosphocreatine; Rats; RNA, Transfer; Spermidine; Spermine; Starvation

1. Phosphoenolpyruvate carboxykinase (GTP) (EC 4.1.1.32) was synthesized by postmitochondrial supernatants of rat liver in the presence of appropriate salts, an energy supply and [(3)H]leucine. Synthesis of enzyme released from polyribosomes was detected by immunoprecipitation with specific antibody followed by electrophoresis of the dissolved antibody-antigen precipitates on sodium dodecyl sulphate-polyacrylamide gels in the presence of a (14)C-labelled enzyme marker. 2. Enzyme synthesis in vitro occurs predominantly on free rather than bound polyribosomes. 3. Starved animals in which de-induction of phosphoenolpyruvate carboxykinase (GTP) had been initiated by re-feeding for 2h had a markedly decreased rate of enzyme synthesis, whether the measurements were made after injection of radioactive leucine into the intact animal or if synthesis was determined in vitro. 4. The low rate of enzyme synthesis by liver polyribosomes from re-fed animals was not due to the absence of soluble factors, nor could it be increased by the addition of cyclic AMP to the protein synthesis system. 5. Phosphoenolpyruvate carboxykinase (GTP) synthesis in vitro is diminished relative to total protein synthesis when the postmitochondrial supernatant is kept at 0 degrees C for several hours before measurement of protein synthesis. Since this effect is blocked by heparin, it is probably caused by selective ribonuclease attack on enzyme mRNA. 6. De-induction of phosphoenolpyruvate carboxykinase (GTP) is tentatively explained as being due to a transcriptional block in specific mRNA synthesis, followed by rapid degradation of existing message.

Topics: Animals; Antibodies; Carbon Radioisotopes; Chemical Precipitation; Cyclic AMP; Enzyme Induction; Guanosine Triphosphate; In Vitro Techniques; Leucine; Liver; Male; Phosphoenolpyruvate Carboxykinase (GTP); Polyribosomes; Rats; Ribonucleases; RNA, Transfer; Starvation; Temperature; Time Factors; Tritium

Topics: Animals; Dose-Response Relationship, Drug; Freeze Drying; Gluconeogenesis; Guanosine Triphosphate; In Vitro Techniques; Kidney; Kidney Cortex; Kidney Tubules; Loop of Henle; Male; Nephrons; Organ Size; Phosphoenolpyruvate Carboxykinase (GTP); Phosphorus Radioisotopes; Rats; Starvation

Topics: Adenosine Triphosphate; Animals; Brain; Carbon Isotopes; Diet; Female; Guanosine Triphosphate; Leucine; Liver; Microsomes; Microsomes, Liver; Nerve Tissue Proteins; Polynucleotides; Pyruvate Kinase; Rats; Rats, Inbred Strains; Ribonucleases; RNA; Starvation; Time Factors; Uridine