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Biomedical subjects

V Felipo

Publications and source records attributed to V Felipo.

At least 109 records · Page 6Linked to original sources
PubMed1988

Paradoxical protection of both protein-free and high protein diets against acute ammonium intoxication.

Rats were fed standard (20% protein), protein-free or high protein (80%) diets for 15 days and then injected intraperitoneally with ammonium acetate (7 mmol/Kg). Survival was 6%, 75% and 100%, respectively, for rats fed standard, protein-free and high protein diets. After injection of 6 mmol/Kg of ammonium acetate, blood ammonia reached a peak (at ca. 2 mM) after 7, 25 and 30 min for rats fed high protein, protein-free and standard diets, respectively. The results presented indicate that protection in the high protein group is due to faster detoxication of ammonia via a more active urea cycle while the tolerance of the protein-free group to higher levels of ammonia remains to be clarified.

Acetates↗
PubMed1988

Long-term ingestion of ammonium increases acetylglutamate and urea levels without affecting the amount of carbamoyl-phosphate synthase.

Rats were fed the following diets: standard (20% protein), high-protein (80%), protein-free, standard plus ammonium and protein-free plus ammonium for six weeks. The standard plus ammonium diet was prepared to contain ammonia equivalent to that supplied by the high-protein diet. Addition of ammonium acetate (20% by mass) to the 20% protein or protein-free diets results in 2.3- and 10-fold increases of urea excretion respectively, without increase of carbamoyl-phosphate synthase. Supplementation of the standard diet with ammonium increases the mitochondrial content of acetylglutamate from 830 to 1590 pmol/mg protein, and of the protein-free diet from 130 to 1040 pmol/mg. However, ingestion of ammonium did not increase the activity of acetylglutamate synthase. Therefore the efflux of acetylglutamate from mitochondria was determined. After 30 min at 37 degrees C liver mitochondria from rats on standard diet released 61% of the initial acetylglutamate while mitochondria from animals on standard plus ammonium diet released only 20%. These results indicate that ingestion of ammonium increases the content of acetylglutamate in rat liver by decreasing its efflux from mitochondria. This effect is similar to that produced in mice by a high protein diet [Morita et al. (1982) J. Biochem. (Tokyo) 91, 563-569]. However, while the high-protein diet increases carbamoylphosphate synthase content, the ammonium diet does not.

Acetyltransferases↗
PubMed1988

Long-term ingestion of ammonium inhibits lysosomal proteolysis in rat liver.

A standard diet was supplemented with ammonium acetate (20%, w/w). The effect on liver protein degradation of oral administration of the ammonium diet to rats for 6 weeks has been studied. It is shown that lysosomal proteolysis is markedly decreased (by 62%) while non-lysosomal proteolysis is inhibited by 11%. This is the first report showing that ammonium ingestion inhibits liver proteolysis.

Acetates↗
PubMed1988

Protective effect of long term ammonium ingestion against acute ammonium intoxication.

Rats were fed for 15 days a diet containing ammonium acetate (20% w/w) and then injected i. p. with ammonium acetate (7 mmol/Kg). Only 1 out of 18 control rats but 9 of 18 rats fed ammonium survived, indicating a protective effect of ammonium ingestion against an acute ammonia challenge. Blood ammonia returned to normal levels sooner in hyperammonemic rats, suggesting more rapid detoxication. In controls, blood urea levels rose immediately reaching a maximum at 15 min, however in hyperammonemic rats urea levels did not change during the first hour, then rose slowly up to 3 hours. These results suggest that in the ammonium fed rats ammonia is initially sequestered and finally eliminated as urea.

Acute Disease↗
PubMed1988

High ammonia levels in brain induce tubulin in cerebrum but not in cerebellum.

Ingestion of large amounts of ammonium increases markedly the content of tubulin in brain. The effect on tubulin induction of ammonium ingestion for up to 100 days was investigated. Brain tubulin content showed a rapid initial increase (28%) at 2 days and reached 50% after 100 days on the diet. To discern if ammonia, the increase in urea synthesis, or both was responsible for tubulin induction, rats were maintained at several levels of uremia (by administering diets containing 0 to 80% protein) or in hyperammonemia (by urease treatment). Only ammonium administration in the diet and urease injection induced tubulin in brain. Tubulin was quantified in three different brain regions. There was a regional selectivity of tubulin induction by ammonia in rat brain. Whereas the cerebellum remained unaltered, the paleencephalon showed the highest increase, and the cerebral cortex exhibited only a modest increase.

Ammonia↗
PubMed1988

Induction of rat brain tubulin following ammonium ingestion.

The effect of oral administration of ammonium acetate for 2, 15, 30, and 100 days on protein synthesis in rat brain was investigated. Although protein synthesis changes were modest, i.e., maximal increase of 24%, there was induction of synthesis and accumulation of a protein with an Mr of 55,000. We show, on the basis of its position on two-dimensional electrophoresis and its immunological reactivity, that this protein is tubulin. Its content increased by 33% as determined by isolation of tubulin after 15 days of oral administration of ammonium and to 49% after 100 days as determined by quantitative immunoblotting.

Acetates↗
PubMed1987

5'-adenosine monophosphate inhibits ternary complex formation by rat liver eIF-2.

The initiation factor 2 (eIF-2) was purified from rat liver essentially to homogeneity. The effect of physiological concentrations of AMP on ternary complex formation by eIF-2 was tested. It is shown that AMP inhibits ternary complex formation (ca. 50% at 100 microM AMP). None of the other adenine-nucleotides tested (ADP, ATP, cAMP, NADH, NAD+ and NADPH) affected ternary complex formation.

Adenine Nucleotides↗
PubMed1987

Retention of actin synthesis in liver under conditions that inhibit synthesis of almost all other proteins.

As briefly reported [(1986) Fed. Proc. 45, 1771, Abstr. 1690], rats fed a protein-free diet for a few days often show a marked inhibition of protein synthesis in liver cytosol. However the synthesis of a protein of molecular mass approximately 42 kDa is fully retained. We show here on the basis of its molecular mass, number of bands on isoelectric focusing, isoelectric point and immunological reactivity that this protein is actin and also that actin mRNA is not degraded by micrococcal nuclease under conditions which degrade the bulk of other mRNAs.

Actins↗
PubMed1986

Precursors of mitochondrial proteins are degraded in the cytosol at different rates.

The stability of rat liver mitochondrial protein precursors in the cytosol was investigated. The precursors were synthesized in a post-mitochondrial supernatant from rat liver, and mitochondria were then added at different times. The amount and pattern of proteins incorporated were determined. The precursors have different rates of transport into mitochondria. Some precursors are stable in the cytosol while most are degraded rapidly, with a half-life of about 30 min at 30 degrees C.

Animals↗
PubMed1986

Rats that consume caffeine show decreased brain protein synthesis.

The effect of caffeine on protein synthesis in brain and liver was studied. When caffeine was added to a post-mitochondrial supernatant from rat brain protein synthesis was inhibited, i.e. 1 mM caffeine about 20%. The effect on protein synthesis of two weeks administration of large doses of caffeine in the drinking fluid of rats was also measured. Caffeine decreased protein synthesis in rat brain by about 32% and 20% compared with "ad libitum" and pair-fed controls. Protein synthesis was calculated taking into account the levels of free leucine determined by HPLC:0.10 mumol/g brain of "ad libitum"; 0.11 for pair-fed and 0.07 for caffeine. The pattern of proteins synthesized was not significantly altered by caffeine as shown by gel-electrophoresis and fluorography. There was no effect on protein synthesis of liver. The possible significance of these results is briefly discussed.

Animals↗
PubMed1986

A rat liver cell-free system for the synthesis of proteins and their transport into mitochondria.

A rat liver cytosol was used to study protein synthesis per se and also to study import of proteins into mitochondria since rat liver cytosol represents an environment closer to that of liver mitochondria than the generally used reticulocytes lysates. Two ATP-regenerating systems were compared. The creatine phosphate/creatine kinase yields higher protein synthesis than the phosphoenol pyruvate/pyruvate kinase system. Hemin, necessary to maintain synthesis by reticulocyte lysates, does not affect the rat liver cytosol. The level of protein synthesis obtained with this cell-free system is comparable to other eukaryotic systems described recently and to the expected value for "in vivo" conditions. Isolated mitochondria incorporated, under our standard conditions, newly synthesized proteins linearly up to 30 min, it ceases when a component(s) in the cytosol had been depleted; addition of freshly translated cytosol restores the import. The bulk of imported proteins are retained in mitoplasts or in mitochondria after treatment with trypsin. The cytosol system will be useful to study questions such as regulation of liver mRNA translation and mitochondrial protein turnover.

Animals↗
PubMed1985

Adenosine 5'-triphosphate stimulates the release of polypeptides from mitochondria.

There was release of polypeptides to the medium when mitochondria containing labeled proteins were incubated with a rat liver post-mitochondrial supernatant. The release of polypeptides increased with the amount of rat liver extract added. Addition of cycloheximide did not inhibit the effect. Heating the post-mitochondrial supernatant did not inhibit the release of mitochondrial proteins, indicating that it was due to a heat-stable factor. The factor responsible has been isolated and identified as ATP. The presence of EDTA inhibits the release of polypeptides caused by ATP and Mg2+ stimulates it. The possible role of ATP in the turnover of mitochondrial proteins is briefly discussed.

Adenosine Triphosphate↗
PubMed1984

Synthesis and transport of the precursor for the beta-subunit of rat liver F1-ATPase.

The synthesis and intracellular transport of the beta-subunit of rat liver F1-ATPase was studied in a cell-free system, using free polysomal mRNA from rat liver and isolated rat hepatocytes. The beta-subunit of rat liver F1-ATPase is synthesized as a larger precursor form in rabbit reticulocyte lysate and then transported into isolated mitochondria in the absence of protein synthesis. In pulse experiments at 37 degrees C, the precursor of the beta-subunit reached a plateau 30 min after the pulse. The labeled mature beta-subunit appeared in the particulate fraction (containing mitochondria) after a time lag and increased almost linearly with time up to 40 min.

Animals↗
PubMed1983

The precursor of rat liver mitochondrial glutamate dehydrogenase has enzymatic activity.

The cytosolic precursor for the mitochondrial glutamate dehydrogenase of rat liver was synthesized in a cell-free reticulocyte lysate using messenger RNA from rat liver. To check whether this precursor had enzymatic activity, a highly sensitive fluorimetric method, which can measure picogram quantities of enzyme, was used together with competitive dissociation of the precursor from an immunoprecipitate with inactive glutamate dehydrogenase. Glutamate dehydrogenase activity, corresponding to that estimated from incorporation of [35S]-methionine, was detected in the precursor. The significance of this finding is discussed.

Animals↗
PubMed1983

Exit of proteins and fragments thereof from mitochondria is accelerated by the import of cytosolic synthesized proteins.

Most mitochondrial proteins are synthesized on cytosolic ribosomes and imported into mitochondria. Incubation of 35S-methionine labeled mitochondria from rat hepatocytes with proteins synthesized in a cell-free system, using messenger RNA from rat liver, dramatically increased the release of mitochondrial proteins and fragments thereof into the medium. Since the synthesized proteins include cytosolic precursors of mitochondrial proteins, our results strongly suggest that import of proteins from the cytosol into mitochondria influences the half-life of proteins in these organelles. The use of this simple approach--i.e. combining the study of protein import and exit with mitochondria--to further clarify intracellular protein turnover and its regulation is suggested.

Animals↗