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Biomedical subjects

E Verney

Publications and source records attributed to E Verney.

At least 55 records · Page 3Linked to original sources
PubMed1984

Nutritional control of protein synthesis. Studies relating to tryptophan-induced stimulation of nucleocytoplasmic translocation of mRNA in rat liver.

Tryptophan has been demonstrated earlier to induce in the livers of rats and mice a rapid stimulation of polyribosomal aggregation and protein synthesis which has been attributed in part to stimulation of translocation of nuclear mRNA into the cytoplasm. This study was concerned with how tryptophan acts to affect the nuclei, particularly the nuclear membranes, in enhancing the nucleocytoplasmic translocation of mRNA of liver cells of rats fasted overnight. The results reveal that tryptophan rapidly becomes incorporated into proteins and also binds to proteins of hepatic cells, particularly proteins of the nuclear envelopes. In vitro binding of 3H-tryptophan to proteins (trichloroacetic-acid-precipitable) of nuclei and cytosols (when incubated together or separately) of livers of tryptophan-treated (10 minutes) rats is increased in comparison with binding to components of control rats. These findings correlate with the enhanced in vitro release of nuclear RNA and the increased activities of nuclear NTPase and protein phosphokinase of the livers of the experimental rats. Preincubation of hepatic nuclei with concanavalin A prevented the increases in in vitro binding of 3H-tryptophan to nuclear proteins, in prelabeled nuclear RNA release, and in nuclear NTPase activity of livers of the tryptophan-treated rats. The results suggest that tryptophan rapidly binds with hepatic proteins (possibly glycoproteins) associated with the nuclear membrane, leading to an increase in the activities of enzymes involved in phosphorylation and dephosphorylation and in release of nuclear mRNA into the cytoplasm.

Amino Acids↗
PubMed1983

Tryptophan-induced stimulation of hepatic ornithine decarboxylase activity in the rat.

The effect of a single tube feeding of L-tryptophan on hepatic ornithine decarboxylase (ODC) activity in rats was investigated. The levels of ODC activity in the livers of control and experimental rats were assayed in vitro by measuring the release of 14CO2 from DL-[1-14C]ornithine. Single tube feedings of varying levels of L-tryptophan (2.5-30 mg/100 g body wt) to overnight-fasted rats 1 hr before sacrifice exhibited increases in the hepatic ODC activities. L-Tryptophan (30 mg/100 g body wt) tube fed to overnight-fasted rats 1/6 to 12 hr before sacrifice induced hepatic ODC activities which were significantly elevated beginning at 1 hr and peaking at 2 hr (6.5-fold increase over controls). In vitro [14C]leucine incorporation into protein using hepatic microsomes of tryptophan-treated rats was significantly increased at 1 hr in comparison with that of controls. The tryptophan-induced stimulation of hepatic ODC activity was not affected by prior adrenalectomy but was abolished by pretreatment with cycloheximide. These studies demonstrate that a single feeding of L-tryptophan can significantly enhance in the rat the activity of ODC, a key enzyme in the biosynthesis of polyamines.

Adrenalectomy↗
PubMed1983

Effect of tryptophan on enzymes and proteins of hepatic nuclear envelopes of rats.

It has been demonstrated earlier that the administration of tryptophan to fasted animals increased the levels of mRNA in the cytoplasm of the liver by stimulating the translocation of nuclear poly(A)-mRNA into the cytoplasm. Also, tryptophan increased the activity of hepatic nuclear envelope (NE) nucleoside triphosphatase, an enzyme considered to be involved in nucleocytoplasmic translocation of mRNA. In this study, the activities of two other NE-associated enzymes, protein phosphokinase and phosphoprotein phosphohydrolase, also implicated in nuclear RNA transport, were investigated in the livers of rats that received a single tube feeding of tryptophan. The administration of tryptophan to fasted rats 10 minutes before killing increased the hepatic NE activities of both enzymes, protein phosphokinase and phosphoprotein phosphohydrolase. Furthermore, tryptophan administration increased the in vivo incorporation of 3H-leucine into NE proteins (+83%) and into other subcellular fractions (+34 to +43%) of the liver compared with that into corresponding fractions of the control rats. Rats that received 3H-leucine to prelabel hepatic proteins and then were treated with puromycin to inhibit further protein synthesis followed by tube feeding of tryptophan revealed greater radioactivity associated with NE proteins than that in controls. These findings suggest that tryptophan may act to stimulate the transport or availability of proteins to the vicinity of the NE, possibly specific regulatory proteins, such as nucleoside triphosphatase, protein phosphokinase and phosphoprotein phosphohydrolase, which show an increase in activity and may then be responsible for the increase in the rate of nucleocytoplasmic translocation of mRNA.

Animals↗
PubMed1981

Effect of elevated dietary tryptophan on protein synthesis in rat liver.

This study investigated whether rats force-fed for three days an elevated (1%) tryptophan diet compared to a control (0.2% tryptophan) diet had changes in hepatic protein metabolism. Earlier, we showed that a single administration of L-tryptophan to fasted rats caused a rapid increase in hepatic protein synthesis. In the present study rats force-fed a high tryptophan diet for 3 days and killed the fourth morning had increased rats of hapatic protein synthesis, cytochrome P-450 and b5 activities, in vitro nuclear RNA release (cell sap and nuclear effects) and nuclear envelope nucleoside triphosphatases activity compared to animals force-fed the control diet. We noted little or no change in hapatic total polyribosomal aggregation patterns or plasma and hepatic free amino acid levels.

Animals↗
PubMed1980

Studies on the influence of tryptophan and related compounds on hepatic polyribosomes and protein synthesis in the rat.

The effect of the administration of L-tryptophan or tryptophan-related compounds on rat liver RNA and protein metabolism was investigated. The five biochemical parameters studied were polyribosomal aggregation, protein synthesis in vitro, synthesis of cytoplasmic poly(A)-mRNA, release of labeled nuclear RNA in vitro (nuclear and cell sap effects) and nuclear envelope nucleoside triphosphatase activity. The administration of L-tryptophan to overnight fasted rats revealed a rapid stimulation in all of the five parameters. Also, some of the tryptophan-related compounds, especially 5-hydroxy-DL-tryptophan, 3-indolepyruvic acid, indole or 3-hydroxyanthranilic acid, revealed stimulation in many of the parameters. However, when rats were pretreated with puromycin to inhibit protein synthesis, only the administration of L-tryptophan was still able to stimulate significantly the hepatic polyribosomes, in vitro protein synthesis, in vitro nuclear RNA release (involving nuclei but not cell sap) and nuclear envelope nucleoside triphosphatase activity. The effects by the other tryptophan-related compounds became inhibited. The results emphasize the unique action of L-tryptophan on hepatic protein synthesis.

3-Hydroxyanthranilic Acid↗
PubMed1980

Studies dealing with hepatic RNA metabolism in rats force-fed a threonine-devoid diet.

Young rats were force-fed for 3 days a purified diet devoid of threonine and a number of aspects relating to RNA metabolism in the livers were studied. The findings in the livers of rats force-fed the threonine-devoid diet in comparison with those force-fed the complete diet were as follows: a) poly(A)-mRNA was increased in nuclei and in polyribosomes; b) DNA-dependent RNA polymerases I and II activities were increased; c) in vitro release of 14C-orotic acid labeled RNA from nuclei revealed that transport was unchanged and nucleoside triphosphatase activity of nuclear envelopes was unchanged; d) polyribosomes (total, free and membrane-bound) shifted toward heavier aggregation and in vitro 14C-leucine incorporation into protein was increased; e) RNase activities (at pH 5.4, 7.6, 9.5) were essentially unaltered; and f) in vivo 14C-choline incorporation into microsomal membranes was increased. By administering selected inhibitors of RNA and protein synthesis, such as actinomycin D, alpha-amanitin or cycloheximide, prior to killing the rats force-fed the threonine-devoid or complete diet for 3 days, it was demonstrated that the stimulatory effect on hepatic polyribosomes and protein synthesis in the experimental group was dependent upon new synthesis of poly(A)mRNA and of protein.

Animals↗
PubMed1980

Acute effect of ethanol on membranes of the endoplasmic reticulum and on protein synthesis in rat liver.

The acute effect of ethanol on the membranes of hepatic endoplasmic reticulum, on the in vitro protein-synthetic activities of hepatic free and membrane-bound polyribosomes and on the plasma proteins of rats fasted overnight was investigated. Ethanol (0.75 g/100 g body weight) was tube-fed as a 50% (v/v) solution in saline 3 hr before sacrifice. Hepatic endoplasmic reticulum membranes from control and ethanol-treated rats were compared using the following techniques: (1) lactoperoxidase-catalyzed radioiodination of proteins and sodium dodecylsulfate-polyacrylamide gel electrophoresis, and (2) measurement of 14C-choline incorporation into membranes. Hepatic microsomal membranes from ethanol-treated rats incorporated in vitro les 125I into total proteins (as well as into the 55,000 molecular weight proteins) and incorporated in vivo less 14C-choline into microsomal membranes than membranes of control rats. Ethanol administration inhibited in vivo incorporation of 14C-leucine or 14C-phenylalanine into liver protein and plasma albumin and globulin. The data also indicate that an acute dose of ethanol reduced the in vitro protein-synthetic activity of hepatic membrane-bound polyribosomes, while free polyribosomes were relatively unaffected.

Animals↗
PubMed1979

Effect of inhibitory and stimulatory agents on protein synthesis in hepatomas and host livers of rats.

Female inbred BUF rats bearing intrahepatically transplanted hepatomas (5123 or 19) were subjected to acute exposure to a variety of hepatotoxic agents (actinomycin D, aflatoxin B1, CCl4, dimethylnitrosamine, ethionine, puromycin, or sparsomycin) or of stimulatory agents (hydrocortisone, phenobarbital, or whole-body X-ray). The responses in terms of changes in polyribosomes and protein synthesis (in vitro and in vivo) of host liver and hepatoma were evaluated. The responses of the host livers and hepatomas to the different agents varied. In general, the host livers responded much more than did the hepatomas. Of the two hepatomas, hepatoma 19 responded less (particularly in terms of polyribosome changes) than did hepatoma 5123. In a few experiments, different doses of actinomycin D, ethionine, or sparsomycin were used and in all instances the host livers responded more than did the hepatomas.

Animals↗