Modification of the host ubiquitome by bacterial enzymes

Attachment of ubiquitin molecules to protein substrates is a reversible post-translational modification (PTM), which occurs ubiquitously in eukaryotic cells and controls most cellular processes. As a consequence, ubiquitination is an attractive target of pathogen-encoded virulence factors. Pathogenic bacteria have evolved multiple mechanisms to hijack the host's ubiquitin system to their advantage. In this review, we discuss the bacteria-encoded E3 ligases and deubiquitinases translocated to the host for an addition or removal of eukaryotic ubiquitin modification, effectively hijacking the host's ubiquitination processes. We review bacterial enzymes homologous to host proteins in sequence and functions, as well as enzymes with novel mechanisms in ubiquitination, which have significant structural differences in comparison to the mammalian E3 ligases. Finally, we will also discuss examples of molecular "counter-weapons" - eukaryotic proteins, which counteract pathogen-encoded E3 ligases. The many examples of the pathogen effector molecules that catalyze eukaryotic ubiquitin modification bring to light the intricate pathways involved in the pathogenesis of some of the most virulent bacterial infections with human pathogens. The role of these effector molecules remains an essential determinant of bacterial virulence in terms of infection, invasion, and replication. A comprehensive understanding of the mechanisms dictating the mimicry employed by bacterial pathogens is of vital importance in developing new strategies for therapeutic approaches.

Effects of vitamins on hepatic nuclear binding of L-tryptophan

This study investigated the in vitro effects of selected vitamins on nuclear L-tryptophan receptor binding of rat liver. Our results revealed that some fat-soluble vitamins, beta-carotene, retinyl acetate, calciferol, alpha-tocopherol, and Trolox, as well as some water-soluble vitamins, thiamine and riboflavin, acted to inhibit in vitro 3H-tryptophan binding to hepatic nuclei. On the other hand, pyridoxine had little or no effect. The addition of dithiothreitol, a protective agent for sulfhydryl groups, along with each vitamin decreased the vitamin's inhibitory effect on in vitro 3H-tryptophan binding to nuclei, with the exception of riboflavin and calciferol. The addition of L-leucine, which alone had no inhibitory effect on in vitro 3H-tryptophan binding to hepatic nuclei but when added with unlabeled L-tryptophan negated the effect of unlabeled L-tryptophan, caused a markedly diminished inhibitory binding effect due to each of the following vitamins, thiamine, beta-carotene, retinyl acetate, and alpha-tocopherol and Trolox, but no effect on riboflavin and calciferol.

Effect of cycloheximide on tryptophan binding to rat hepatic nuclei

This study evaluated whether cycloheximide, an inhibitor of protein synthesis, would affect the binding of L-tryptophan to rat hepatic nuclei or nuclear envelopes. Previous reports have indicated that the binding of L-tryptophan to hepatic nuclear envelope protein was saturable, stereospecific, and of high affinity. Also, the administration of L-tryptophan rapidly stimulated hepatic protein synthesis. In this study, we determined that the addition of cycloheximide in vitro inhibited 3H-tryptophan binding to hepatic nuclei or nuclear envelopes. Heat-treated cycloheximide failed to have this inhibitory binding effect. In vivo treatment of rats with cycloheximide diminished in vitro 3H-tryptophan binding to hepatic nuclei of treated rats compared to controls. Puromycin, another inhibitor of hepatic protein synthesis, when added in vitro did not affect 3H-tryptophan binding to hepatic nuclei but did diminish in vitro binding after in vivo treatment. Thus, cycloheximide added in vitro diminished 3H-tryptophan binding to hepatic nuclei probably by its structural effect on the receptor while cycloheximide administered in vivo may also act in part by inhibiting protein synthesis.

Effects of altered tonicity by sodium chloride on L-tryptophan binding to hepatic nuclei

This study was concerned with the effects of NaCl administered in vivo or added in vitro to isolated nuclei on [(3)H]tryptophan binding to rat hepatic nuclei assayed in vitro. Hypertonic (10.7%) NaCl administered in vivo to rats caused at 10 min a marked decrease in in vitro binding (total and specific) of [(3)H]tryptophan to hepatic nuclei. In vitro incubation of isolated hepatic nuclei, but not of isolated nuclear envelopes, with added NaCl (particularly at 0.125 x 10(-4) M and 0.25 x 10(-4) M) revealed significant inhibition of [(3)H]tryptophan binding. However, isolated hepatic nuclear envelopes prepared after in vitro incubation of isolated nuclei with added NaCl did show inhibition of [(3)H]tryptophan binding (total and specific) compared with controls. Other salts (KCl, MgCl(2), NaHCO(3), NaC(2)H(3)O(2), NaF, or Na(2)SO(4)), at similar concentrations to that of NaCl except for MgCl(2), when added to isolated nuclei did not appreciably inhibit nuclear tryptophan binding. Kinetic studies of in vitro nuclear [(3)H]tryptophan binding in the presence of 0.125 x 10(-4) M NaCl revealed that binding decreased at 0.5 h and continued to 2 h compared with nuclear [(3)H]tryptophan binding with controls (without NaCl addition). The results obtained in vivo in rats and those obtained in vitro with isolated hepatic nuclei revealed NaCl-induced inhibitory effects on [(3)H]tryptophan binding to hepatic nuclei. Although the inhibitory effects were similar under the two different experimental conditions, the mechanism for each may be different in that the NaCl concentration in hepatic cells after administration of NaCl in vivo was appreciably higher than the low levels added in vitro to the isolated hepatic nuclei.

Hormonal influences on tryptophan binding to rat hepatic nuclei

We evaluated whether selected hormones, 3,5,3'-triiodothyronine (T3), hydrocortisone (HC) or insulin, would influence the binding (saturable, stereospecific, and of high affinity) of L-tryptophan to rat hepatic nuclei or nuclear envelopes. T3 (10(-14) to 10(-10) M) appreciably inhibited in vitro L-(5-3H) tryptophan binding to hepatic nuclei and T3 (10(-16) to 10(-4) M) appreciably ameliorated the inhibitory effect of unlabeled tryptophan (10(-4) M) on such binding. In vivo tryptophan administration (1 h) stimulated hepatic protein synthesis but the addition of T3 negated such stimulation. HC (10(-12) to 10(-4) M) did not affect and insulin (10(-16) to 10(-4) M) had only a small inhibitory effect on 3H-tryptophan binding to hepatic nuclei, but each (10(-12) to 10(-4) M) when added to unlabeled tryptophan (10(-4) M) diminished the inhibitory binding effect of unlabeled tryptophan alone. Thus, T3 competes with tryptophan for hepatic nuclear tryptophan binding and also negates tryptophan's stimulatory effect on hepatic protein synthesis.

Influence of lead acetate and selected metal salts on tryptophan binding to rat hepatic nuclei

This study evaluated whether lead acetate or other selected metal salts would influence the binding of L-tryptophan to rat hepatic nuclei. Lead salts and other salts of cadmium, zinc, mercury, and molybdenum, when added alone, had only small effects on 3H-tryptophan binding to hepatic nuclei in vitro. However, each of these salts, when added along with unlabeled L-tryptophan (excess, 10(-4) M), caused significantly less inhibition of 3H-tryptophan binding to hepatic nuclei than did unlabeled L-tryptophan alone. Lead acetate (10(-10) to 10(-4) M), when added along with unlabeled L-tryptophan, abrogated the inhibition of binding related to unlabeled L-tryptophan alone. Sodium arsenite (but not potassium arsenate) as well as sodium selenite (at 10(-4) M concentrations) inhibited to a moderate degree the in vitro 3H-tryptophan binding to hepatic nuclei, but addition of 10(-4) dithiothreitol, a protective agent for sulfhydryl groups, diminished this inhibition. Rats receiving a high dose of lead acetate before being tube-fed L-tryptophan displayed a decrease in hepatic protein synthesis compared with the stimulatory response connected with L-tryptophan alone. Thus, the addition of lead acetate and of other metal salts appears to have an inhibitory effect on L-tryptophan binding to hepatic nuclei. Lead acetate was investigated in in vivo experiments and was found to negate the stimulation of hepatic protein synthesis related to L-tryptophan alone.

Hormonal influences on tryptophan binding to rat hepatic nuclei

This study evaluated whether selected hormones, 3,5,3'-triiodothyronine (T3), hydrocortisone (HC), or insulin, would influence the binding of L-tryptophan to rat hepatic nuclei or nuclear envelopes. The first two hormones have nuclear receptors that belong to the same superfamily, while insulin belongs to a different unrelated superfamily of receptors. Previous reports have indicated that the binding of L-tryptophan to hepatic nuclear proteins was saturable, stereospecific, and of high affinity. Also, previous studies showed that administration of L-tryptophan rapidly stimulated hepatic protein synthesis. In this study, we investigated whether each hormone alone or together with unlabeled tryptophan would influence tryptophan binding to rat hepatic nuclei or nuclear envelopes as assayed by in vitro L-5-(3)H-tryptophan binding. Our results indicate that T3 10(-14) to 1(-10) mol/L appreciably inhibited in vitro 3H-tryptophan binding to hepatic nuclei and T3 10(-16) to 10(-4) mol/L appreciably ameliorated the inhibitory effect of unlabeled tryptophan (10(-4) mol/L) on in vitro 3H-tryptophan binding. In vivo administration (1 hour) of tryptophan alone stimulated hepatic protein synthesis, but addition of T3 negated such stimulation. Addition of HC 10(-12) to 10(-4) mol/L had no effect and addition of insulin 10(-16) to 10(-4) mol/L had only a small inhibitory effect on in vitro 3H-tryptophan binding to rat hepatic nuclei, but each (10(-12) to 10(-4) mol/L), when added to unlabeled tryptophan (10(-4) mol/L), diminished the inhibitory binding effect of unlabeled tryptophan alone. Our study indicates that T3 competes with tryptophan for hepatic nuclear tryptophan binding, and it also appears to negate tryptophan's stimulatory effect on hepatic protein synthesis.

Mouse strain and source of L-tryptophan affects hepatic nuclear tryptophan binding

This study describes that the affinity for specific L-tryptophan binding to hepatic nuclei in vitro is markedly decreased in NZBWF1 mice in comparison to that in Swiss mice. Also, the hepatic nuclei of NZBWF1 mice have a significantly decreased binding response in vitro to Showa Denko L-tryptophan (implicated in the eosinophilia-myalgia syndrome) or to its contaminants, 1,1'-ethylidenebis(tryptophan) or 3-phenylamino-L-alanine, when each is added to control, non-implicated L-tryptophan compared with hepatic nuclei of Swiss mice. Enhanced hepatic protein synthesis induced by tube-feeding control L-tryptophan is much less in NZBWF1 mice than in Swiss mice. Tube-feeding of Showa Denko L-tryptophan induced less stimulation of hepatic protein synthesis than did control L-tryptophan in Swiss mice but essentially none in NZBWF1 mice. NZBWF1 mice have a genetically altered response to L-tryptophan which may prove to be useful is studying the role of L-tryptophan in health and in disease.

Differences in tryptophan binding to hepatic nuclei of NZBWF1 and Swiss mice: insight into mechanism of tryptophan's effects

We have observed that in NZBWF1 mice the affinity for L-tryptophan binding to hepatic nuclei in vitro is markedly less than that of Swiss mice. In vitro binding of [3H]tryptophan to hepatic nuclei from both strains was determined without and with unlabeled L-tryptophan (10(-4) mol/L). The relative specific binding of L-tryptophan to hepatic nuclei in vitro was 60.9 +/- 4.4% for Swiss mice and 35.8 +/- 5.4% (P < 0.01) in NZBWF1 mice. The total specific binding (bound radioactivity/mg nuclear protein) of L-tryptophan to hepatic nuclei in vitro was 74.9% (P < 0.05) lower in NZBWF1 mice than in Swiss mice. Other strains (DBA, SJL and BALB/c) had specific binding affinities similar to that of Swiss mice. Serum and hepatic free tryptophan concentrations and hepatic tryptophan dioxygenase activity in mice that were food-deprived overnight or 1 h after tube-feeding L-tryptophan (20 mg/100 g body weight) were similar in the strains of mice. In vitro [14C] leucine incorporation into protein using hepatic microsomes of mice 1 h after tube-feeding L-tryptophan (20 mg/100 g body weight) revealed a significantly greater (P < 0.05) increase relative to food-deprived controls in Swiss mice (76.8 +/- 19.2%) than the increase in NZBWF1 mice (26.5 +/- 2.6%). Nuclear [14C]-labeled RNA release in vitro was increased 77.2 +/- 18.0% by tube-feeding of L-tryptophan in Swiss but only 7.6 +/- 5.8% (P < 0.02) in NZBWF1 mice. Liver nuclear poly(A)-polymerase and nucleoside triphosphatase activities were variably increased by the administration of L-tryptophan in both strains. In summary, compared with Swiss mice, NZBWF1 mice have a lower specific binding affinity for L-tryptophan by hepatic nuclei, and this alteration may account for the other differences in responses to L-tryptophan by the two strains.

Toxic effect of valproic acid on tryptophan binding to rat hepatic nuclei

This study evaluated whether valproic acid, a branched-chain fatty acid which has been used in the treatment of seizures, would influence the binding Of L-tryptophan to rat hepatic nuclei. Previous studies have indicated that binding of L-tryptophan to hepatic nuclear envelope protein was saturable, stereospecific, and of high affinity. In this study, we investigated whether valproic acid, which under certain conditions is heptatoxic, would influence L-tryptophan binding to rat hepatic nuclei as assayed by in vitro L-(5-3H)tryptophan binding. Our results indicate that the addition of valproic acid to hepatic nuclei or nuclear envelopes in vitro has little influence on their L-(5-3H)tryptophan binding. On the other hand, when valproic acid (80 mg/100 g body weight) is tube-fed 2 h before killing, the isolated nuclei show decreased specific L-tryptophan binding (total binding minus non-specific binding using unlabeled L-tryptophan (10(-4)M), at 2000-fold excess) compared with controls. Other fatty acids (oleic, palmitic or linoleic acid at 10(-4)M) when added with excess, unlabeled L-tryptophan (10(-4)M) in vitro to hepatic nuclei revealed some (but less than with valproic acid) decreased specific binding compared with controls. At high doses, valproic acid (80 mg/100 g body weight) appears to decrease tryptophan-induced stimulation of hepatic protein synthesis, probably in a hepatotoxic manner.

Comparative studies on tryptophan binding to hepatic nuclear envelopes in Sprague-Dawley and Lewis rats

Since Lewis rats are susceptible to many inflammatory diseases and have been used in an experimental model of the eosinophilia-myalgia syndrome, we investigated whether Lewis rats would respond to L-tryptophan as have Sprague-Dawley rats reported earlier. In this comparative study using females of both strains, we observed a decrease in the affinity of in vitro L-tryptophan binding to hepatic nuclei and nuclear envelopes of Lewis rats compared with Sprague-Dawley rats. However, in vivo stimulatory effects of administering L-tryptophan on hepatic polyribosomal aggregation, protein synthesis, and nuclear RNA release were similar in both strains. In vitro [3H]tryptophan binding to hepatic nuclear envelopes, using L-tryptophan implicated in cases of the eosinophilia-myalgia syndrome, revealed less specific binding than when using nonimplicated L-tryptophan in both strains. The possible significance of the quantitative difference in the binding affinity of L-tryptophan to hepatic nuclei of Lewis rats compared with those of Sprague-Dawley rats is as yet undetermined.

Indolic compounds affect tryptophan binding to rat hepatic nuclei

This study evaluates the effects of indolic or indole-related compounds on binding of L-tryptophan (saturable, stereospecific and of high affinity) to rat hepatic nuclei or nuclear envelopes. Addition of any one of many indolic or indole-related compounds, and particularly of 3-methylindole, does not inhibit in vitro binding of [3H]tryptophan to hepatic nuclear envelopes. However, when 3-methylindole (10(-10) to 10(-4) mol/L) is added in combination with unlabeled L-tryptophan (10(-4) mol/L), it diminishes the inhibitory effect of unlabeled L-tryptophan alone. Scatchard analysis of the binding affinities of in vitro [3H]tryptophan binding to hepatic nuclear envelopes using L-tryptophan in the absence or presence of 3-methylindole reveals similar dissociation constants (KD) under the two conditions, but the binding concentrations (Bmax) were greater in the combined group compared with that in the L-tryptophan alone group. Addition of 3-methylindole to liver before homogenization decreases specific [3H]tryptophan binding to nuclei compared with controls (without addition). L-Tryptophan tube-fed to rats with or without 3-methylindole administration increases in vitro hepatic protein synthesis compared with that of saline tube-fed controls. 3-Methylindole itself does not affect protein synthesis. Our report describes the effects of 3-methylindole on specific tryptophan binding to hepatic nuclear envelope receptor and discusses the possible implications thereof.

Studies with 1,1'-ethylidenebis(tryptophan), a contaminant associated with L-tryptophan implicated in the eosinophilia-myalgia syndrome

L-Tryptophan binds to a rat liver nuclear envelope protein, and this binding is saturable, stereospecific, and of high affinity. Utilizing an in vitro assay of [3H]tryptophan binding to rat hepatic nuclear envelopes, we have previously determined that the L-tryptophan obtained from Showa Denko and which was implicated in cases of the eosinophilia-myalgia syndrome (EMS) inhibited [3H]tryptophan binding differently than did control L-tryptophan (not implicated in EMS). Therefore, in this study we investigated whether the addition of 1,1'-ethylidenebis(tryptophan) (EBT), a contaminant or impurity in L-tryptophan implicated in EMS, would have an effect. Our results indicate that EBT alone has little inhibitory binding effect compared with that of control L-tryptophan and that when EBT was added to control L-tryptophan the inhibitory binding effort was similar to that of control L-tryptophan alone. On the other hand, in vitro addition of EBT plus L-tryptophan to nuclei of cultured murine macrophages (WLG5) results in less inhibition of [3H]-tryptophan binding than does addition of L-tryptophan alone. Similar in vitro additions to nuclei of rat brain reveal little effect on binding, as was also the case for hepatic nuclear envelopes. Adding EBT to an in vitro hepatic protein synthesis system and measuring [3H]tryptophan incorporation into acid-precipitable proteins reveal that it competes similarly to that found with equimolar concentrations of unlabeled L-tryptophan. It does not affect [14C]leucine incorporation into proteins. [14C]EBT becomes incorporated in vitro into proteins (acid-precipitable), and this incorporation is diminished in the presence of equimolar concentrations of unlabeled EBT or L-tryptophan. This suggests that EBT or possibly a breakdown product becomes incorporated into proteins. Speculation as to how EBT may affect tissues in experimental animals is presented.

Effect of 3-phenylamino-L-alanine on tryptophan binding to rat hepatic nuclear envelopes

We have determined that the addition of 3-phenylamino-L-alanine (PAA), a recently reported contaminant in L-tryptophan implicated in the eosinophilia-myalgia syndrome, affects tryptophan binding by utilizing an in vitro measurement of 3H-tryptophan binding to hepatic nuclei or nuclear envelopes. PAA (10(-10) to 10(-4) M) diminishes the inhibitory effect of binding due to excess unlabeled L-tryptophan (10(-4) M). PAA alone has no inhibitory effect on binding. The effect of PAA on in vitro tryptophan binding is in contrast to that of another contaminant, 1,1'-ethylidenebis(tryptophan), which together with excess unlabeled L-tryptophan does not appreciably affect the binding. In vitro addition of PAA and L-tryptophan to nuclei of rat brain or of cultured murine macrophages does not affect [3H]tryptophan binding in comparison to L-tryptophan alone as is the case with hepatic nuclear envelopes. Adding PAA to an in vitro protein synthesis system and measuring [3H]tryptophan or [3H]alanine incorporation into acid-precipitable proteins reveals that it competes similarly, but somewhat less, than does equimolar concentrations of unlabeled L-tryptophan or L-alanine, respectively. This suggests that PAA or a breakdown compound becomes incorporated into proteins. Speculation as to how PAA may affect tissues in experimental animals is presented.

Effect of metyrapone on tryptophan binding to rat hepatic nuclei

This study evaluated whether metyrapone (2-methyl-1,2-di-3-pyridyl-1-propanone), an inhibitor of endogenous adrenal corticosteroid synthesis via inhibition of cytochrome P-450-mediated steroid hydroxylation, would influence the binding of L-tryptophan to rat hepatic nuclei or nuclear envelopes. Previous publications have indicated that binding of L-tryptophan to hepatic nuclear envelope proteins was saturable, stereospecific, and of high affinity. In this study, we investigated whether metyrapone would influence L-tryptophan binding to rat hepatic nuclei or nuclear envelopes as assayed by in vitro L-(5-3H)tryptophan binding. Our results indicate that the addition of metyrapone in vitro has little influence on L-(5-3H)tryptophan binding to hepatic nuclei or nuclear envelopes. On the other hand, when metyrapone (1 mg/100 g body weight) is tube-fed 30 minutes before killing, the isolated hepatic nuclei show decreased specific L-tryptophan binding (total binding minus nonspecific binding [using 2,000-fold excess of unlabeled L-tryptophan]) compared with controls. Also, addition of metyrapone in vitro to rat liver before homogenization and preparation of nuclei caused the nuclei to show decreased specific tryptophan binding compared with controls. Under these in vitro conditions, SKF 525A, another inhibitor of hydroxylation, showed inhibitory effects similar to those of metyrapone. Thus, metyrapone can interfere with rat liver nuclear envelope receptor binding to L-tryptophan, and possibly acts via its effects on hydroxylation. At high doses, metyrapone (20 mg/100 g body weight) appears to inhibit tryptophan-induced stimulation of hepatic protein synthesis.

Tryptophan binding to nuclei of rat brain

Nuclei purified from whole rat brain specifically bind [3H]tryptophan ([3H]Trp) under in vitro conditions. Excess unlabeled Trp (10(-4) M) is an effective inhibitor of in vitro [3H]Trp binding to brain nuclei. Rats tube-fed L-tryptophan (Trp) (30 mg/100 g body wt) 30 min to 4 hr before killing revealed decreased specific binding of [3H]Trp to purified brain nuclei in vitro. By Scatchard analysis, the nuclei from whole brain appear to contain one binding site for [3H]Trp, and the KD is 263 nM. A number of Trp-related compounds, Trp metabolites, or other amino acids and their analogues were observed to compete for in vitro [3H]Trp binding to brain nuclei. The ability of Trp analogues, metabolites, and other cognate compounds to inhibit in vitro [3H]Trp binding to brain nuclei was evaluated and utilized to map the active site of Trp binding.

Competitive studies relating to tryptophan binding to rat hepatic nuclear envelopes as a sensitive assay for unknown compounds

Our laboratory has reported that L-tryptophan binds to a rat liver nuclear envelope protein and this binding is saturable, stereospecific and of high affinity. Utilizing an in vitro [3H]tryptophan binding assay to hepatic nuclear envelopes, we have determined the effects of using excess unlabeled L-tryptophan from a number of different suppliers. This study reports that, based on our in vitro binding assay, some significant differences were observed when implicated L-tryptophan in cases of the eosinophilia-myalgia syndrome obtained from a Japanese manufacturer, Showa Denko, was assayed, in contrast to non-implicated L-tryptophan from other suppliers. An isolated impurity of Showa Denko L-tryptophan, 1,1'-ethylidenebis(tryptophan) alone or together with non-implicated L-tryptophan or its breakdown product, 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, did not appreciably affect the in vitro [3H]tryptophan binding to hepatic nuclear envelopes as did the Showa Denko L-tryptophan. Our data, derived with our in vitro binding assay system, suggests that implicated L-tryptophan from Showa Denko contains a compound/s (unknown at present) other than 1,1'-ethylidenebis(tryptophan), which alters in vitro [3H]tryptophan binding. The significance of the impurity/ies involved remains to be determined.

Inhibitory effect of demoxepam on tryptophan binding to rat hepatic nuclei

Since some patients with eosinophilia-myalgia syndrome ingested tryptophan along with benzodiazepines, we investigated whether demoxepam, the N-desalkylated compound of chlordiazepoxide, would influence the binding of tryptophan to hepatic nuclei. L-Tryptophan has been shown to bind (saturable, stereospecific, and of high affinity) to rat hepatic nuclei and nuclear envelopes. We report that demoxepam has an inhibitory effect on in vitro [3H]tryptophan binding to rat hepatic nuclei and has an apparent KD approximately 22 microM.

Effect of benzodiazepines on tryptophan binding to rat hepatic nuclei

This study evaluates whether or not some of the benzodiazepines would influence the binding of L-tryptophan to rat hepatic nuclei or nuclear envelopes. Previous publications have indicated that binding of L-tryptophan to hepatic nuclear envelope proteins was saturable, stereospecific, and of high affinity. In this study, we investigated whether some of the benzodiazepines would influence L-tryptophan binding to rat hepatic nuclei or nuclear envelopes as assayed by in vitro L-(5-3H) tryptophan binding. Our results indicate that the addition of chlordiazepoxide, diazepam, prazepam, flurazepam, nordazepam, N-desalkylflurazepam, temazepam, oxazepam, lorazepam, or 4-chlorodiazepam has little influence on the L-(5-3H) tryptophan binding to hepatic nuclei in vitro. However, the addition of demoxepam, the N-desalkylated compound of chlordiazepoxide, caused marked competition with 3H-tryptophan binding to hepatic nuclei in vitro. When chlordiazepoxide (1 mg/100 g body weight) is administered intraperitoneally 20 min before killing, the isolated hepatic nuclei reveal decreased specific L-tryptophan binding compared to controls. Also, rats pretreated with chlordiazepoxide intraperitoneally before tube-feeding L-tryptophan revealed diminished tryptophan-induced hepatic nuclear RNA efflux and protein synthesis. Our results suggest that chlordiazepoxide, possibly by itself or through a metabolite, can act to affect hepatic nuclear binding of L-tryptophan and to inhibit the stimulatory effect of L-tryptophan on hepatic protein synthesis.

Studies with Compounds that Compete with Tryptophan Binding to Rat Hepatic Nuclei

Tryptophan has been demonstrated to affect hepatic RNA and protein metabolism. Binding of tryptophan to nuclear envelope proteins has been demonstrated to be saturable, stereospecific, and of high affinity. The hepatic nuclear envelope tryptophan binding protein (glycoprotein) has been purified to apparent homogeneity using either concanavalin A-agarose or tryptophan-agarose. The receptor has an Mr of approximately 34,000, which is the same as that observed when [3H]tryptophan has been crosslinked to nuclear proteins. In this study, we investigated whether analogs, metabolites or related compounds of tryptophan as well as other amino acids may bind to rat hepatic nuclei using in vitro [3H]tryptophan binding assays. Our results indicate that compounds that compete with [3H]tryptophan binding to hepatic nuclei or nuclear envelopes contain the alpha-amino-propionic acid structure. Such compounds were 5-fluoro tryptophan, 7-aza tryptophan, 5-hydroxy tryptophan, alanine, phenylalanine, tyrosine, cysteine and cystine. It was of interest that, whereas tryptophan-methyl ester and tryptophan-ethyl ester competed, alpha-methyl tryptophan, N-formyl tryptophan, N-acetyl tryptophan, and N-methyl tryptophan did not compete with [3H]tryptophan binding to hepatic nuclei or nuclear envelopes. Nonetheless, only the in vivo administration of L-tryptophan was able to stimulate nucleocytoplasmic efflux of hepatic RNA and protein synthesis.

Comparison of effects of L-tryptophan and a tryptophan analog, D,L-beta-(1-naphthyl)alanine, on processes relating to hepatic protein synthesis in rats

Earlier studies reported that the administration of L-tryptophan increased polyribosomal aggregation, protein synthesis and levels of cytoplasmic poly(A) mRNA in rat liver. This study was concerned with the effects of an L-tryptophan analog, D,L-beta-(1-naphthyl)alanine, in comparison with those of L-tryptophan. Both D,L-beta-(1-naphthyl)alanine and L-tryptophan bound to the L-tryptophan receptor protein and increased poly(A)polymerase and nucleoside triphosphatase activities of hepatic nuclei. However, only L-tryptophan was associated with increases in the release of labeled nuclear RNA (in vitro), in protein synthesis, in polyribosomal aggregation and in glycosylation ([14C]glucosamine incorporation into proteins) of rat liver. These results indicate that although D,L-beta-(1-naphthyl)alanine affected hepatic nuclei (binding and enzyme levels), it did not stimulate nucleocytoplasmic translocation of mRNA and concomitant protein synthesis, as did L-tryptophan.

Effect of feeding a choline-deficient diet on the hepatic nuclear response to tryptophan in the rat

In earlier studies the acute administration of tryptophan (TRP) to rats was reported to induce enhanced in vivo [14C]orotate-labeled hepatic nuclear RNA release in vitro. This change was considered to possibly be related to the induction of more and larger gamma-glutamyl transpeptidase-positive foci in the livers of rats treated with diethylnitrosamine and fed long-term elevated TRP in a choline-supplemented (CS) but not in a choline-deficient (CD) diet (comparisons with respective controls). In this study we investigated whether feeding a CD compared to a CS diet for 1 week would affect selected hepatic nuclear responses to TRP. Rats fed the CS but not the CD diet and tube-fed TRP 10 min before being killed revealed enhanced labeled hepatic nuclear RNA release in vitro. In all experiments, comparisons were made with the control groups (rats fed the CS or stock diet). When rats were fed elevated TRP (2%) in the diets (CS or CD) for 1 week, labeled hepatic nuclear RNA release was increased with the CS + TRP but not with the CD + TRP diet group. [3H]TRP binding to hepatic nuclei in vitro revealed no change in the CS + TRP group, decreased in the CD group, and markedly increased in the CD + TRP group in comparison with the control (CS) group. Hepatic nuclear nucleoside triphosphatase activity was increased only in the CS + TRP group while hepatic nuclear poly(A) polymerase activity was increased in the CS + TRP and in the CD +/- TRP groups. Serum cholesterol and triglycerides were decreased in the CD group and increased to control levels in the CD + TRP group.

Nuclear envelope glycoprotein with poly(A) polymerase activity of rat liver: isolation, characterization, and immunohistochemical localization

A protein with poly(A) polymerase activity has been identified and isolated from hepatic nuclear envelopes of rats to near homogeneity. The ability of the enzyme to bind to concanavalin A-agarose and to be eluted from the column with methyl alpha-D-mannopyranoside (0.2 M) as well as the inhibitory effects of alpha-mannosidase suggested that it was a glycoprotein. Poly(A) polymerase has an absolute requirement for a divalent cation, ATP, and an oligonucleotide primer. The enzyme activity with Mn2+ was about 20-fold higher than that with Mg2+. Several known inhibitors adversely affected poly(A) polymerase activity. The enzyme has a molecular weight of 64,000 when analyzed by polyacrylamide gel electrophoresis under denaturing conditions and has a sedimentation coefficient of 4.5 S. Immunohistochemical studies using polyclonal antibodies raised against the purified enzyme revealed that the antigen was localized in the nuclear membranes.

Poly(A) polymerase activity in murine serum. Elevation in animals with proliferative changes

Sera of normal rats contain polynucleotide adenylyltransferase [poly(A) polymerase] activity. The enzymatic activity has been optimized with regard to primer concentration, ion requirements, kinetics, and protein. Results based on inclusion of inhibitors in the assay system show that the enzyme is poly(A) polymerase. High levels of the enzymatic activity were prevalent in sera of (a) BUF/SimfBR rats bearing sc transplanted hepatomas; (b) Sprague-Dawley rats with hepatoma cells grown in ascites; (c) partially hepatectomized Sprague-Dawley rats; and (d) MRL/lpr mice, which are in a massive lymphoproliferative autoimmune state.

Identification and immunohistochemical localization of a tryptophan binding protein in nuclear envelopes of rat liver

A tryptophan binding protein which was identified by binding studies has been purified to apparent homogeneity from rat liver nuclear envelopes. Two affinity matrices, namely, concanavalin A-agarose and tryptophan-agarose, were utilized for purification of the binding protein. Findings with lectin affinity chromatography suggested that the binding entity was a glycoprotein since it could be eluted off the column with methyl alpha-D-mannopyranoside (0.2 M). Eluates from both columns, when electrophoresed separately (under denaturing conditions) on polyacrylamide gels, revealed the presence of a protein with an apparent molecular weight of approximately 33,000-34,000 which is the same as that observed when covalently bound (i.e., crosslinked) [3H]-tryptophan is analyzed on polyacrylamide gels under denaturing conditions and then autoradiographed. Polyclonal antibodies raised against the binding protein recognized polypeptides with molecular weights of 64,000 and 33,000-34,000 when analyzed by the Western blot technique, suggesting that the protein was probably a dimer. Immunohistochemical studies revealed that the antigen is localized in the nuclear membranes, thereby corroborating our biochemical premise that the binding protein was present in the nuclear envelopes.

Effect of tryptophan on toxic cirrhosis induced by intermittent carbon tetrachloride intoxication in the rat

The effects of the administration of tryptophan on toxic cirrhosis induced by intermittent carbon tetrachloride (CCl4) intoxication in the rat were investigated. Rats received CCl4 (0.45 ml/100 g body wt ip) twice weekly for 10-14 weeks. Tryptophan (30 mg/100 g body wt) by stomach tube was administered 1 hr before killing. Tryptophan improved hepatic polyribosomal aggregation and [14C]leucine incorporation into protein in vitro of control rats as well as long-term CCl4-treated rats that had developed toxic cirrhosis. However, the effects were more marked in control than in experimental rats. Tryptophan administration induced an increase in labeled nuclear RNA release in vitro and a decrease in labeled tryptophan binding to nuclear protein in vitro of livers of rats receiving long-term CCl4 and of control rats. The results indicate that the stimulatory effects of a single administration of tryptophan in toxic cirrhotic livers are similar to, but somewhat less than, those which occur in livers of normal, control rats.

Effect of tryptophan on livers of pregnant and lactating rats and their fetuses and pups

The effect of the administration of L-tryptophan on hepatic polyribosomes and protein synthesis in pregnant rats and their fetuses and in lactating rats and their pups was investigated. Pregnant rats tube-fed tryptophan 1 hr before killing revealed increased hepatic protein synthesis but essentially unmodified polyribosomal aggregation of maternal livers while no changes were observed in fetal livers in comparison to controls (water-treated). Lactating rats tube-fed tryptophan 1 hr before killing revealed increased polyribosomal aggregation and protein synthesis of the livers in comparison to controls. Pups of these mothers that received tryptophan intraperitoneally 1 hr before killing did not reveal a significant change in the hepatic polyribosomes or protein synthesis.

Effect of tryptophan on isolated hepatocytes of rats

The addition of tryptophan to adult rat hepatocyte cultures stimulated DNA synthesis. The increase in DNA synthesis as measured by 3H-thymidine incorporation into DNA was observed on treatment of the cultures with tryptophan for 48 h but also as short as for 6 h in comparison with control cultures. An increase was also apparent at 30 h which was maintained for up to 48 h post treatment with tryptophan. The increase in DNA synthesis by tryptophan cannot be attributed to cell injury or to increased DNA degradation. Of the degradative enzymes added after harvesting the hepatocytes, only DNase decreased incorporation of 3H-thymidine. The observed effect was specific for tryptophan since treatment with kynurenine, isoleucine, methionine or serine failed to show a significant effect. Pretreatment of cultured hepatocytes with hydroxyurea prevented the tryptophan stimulated increase in DNA synthesis suggesting that the latter was due to replicative and not to reparative DNA synthesis. Experiments performed with the addition of diethylnitrosamine also alluded to tryptophan's role in replicative DNA synthesis. The mechanism of tryptophan-induced DNA synthesis is discussed.

Influence of level of dietary protein on tryptophan-induced promotional activity in induction of gamma-glutamyl transpeptidase-positive foci of rat liver

The influence of varying the dietary protein content on the emergence of gamma-glutamyl transpeptidase (GGT)-positive foci in the livers of male rats fed elevated (2%) L-tryptophan (TRP) after being exposed to a hepatocarcinogen was investigated. Subtotal hepatectomies were performed, and 18 hr later the rats were treated with diethylnitrosamine (30 mg/kg). Ten days later four dietary groups were followed for 10 weeks: (1) control diet containing 21% protein (C); (2) control diet containing 5.3% protein (C-LP); (3) C + TRP; and (4) C-LP + TRP. Rats fed the C-LP diet developed heavier livers but fewer and smaller GGT + foci than did rats fed the C diet. Rats fed elevated TRP diets (C + TRP and C-LP + TRP) developed more and larger GGT + foci than did rats fed the regular control diets (C and C-LP), indicating that the promotional effect of elevated dietary TRP was similar at the two levels of dietary protein.

The influence of hypertonic NaCl on nucleocytoplasmic translocation of RNA in the rat liver

Hypertonic NaCl administered to rats or mice has been demonstrated to induce in the liver a rapid disaggregation of polyribosomes and inhibition of protein synthesis. This study was concerned with whether hypertonic NaCl would affect nucleocytoplasmic translocation of RNA in the livers of rats. The effect of tube-feeding a hypertonic (10.7%) NaCl solution (321 mg in 3 ml/100 g body wt) for 10 minutes on in vitro release of 14C-orotate-labeled nuclear RNA was assayed. Although the combination of nuclei and cytosols of livers of hypertonic NaCl-treated rats revealed diminished in vitro labeled nuclear RNA release in comparison with hepatic nuclei and cytosols of control (water-treated) rats, each of the two components varied in activity. Even though the overall effect was an inhibitory one, cytosols of livers of hypertonic NaCl-treated rats stimulated in vitro release of labeled nuclear RNA, whereas nuclei of livers of hypertonic NaCl-treated rats revealed diminished in vitro release of labeled nuclear RNA in comparison with cytosols and nuclei of livers of control rats. The stimulatory effect of the hepatic cytosols of the hypertonic NaCl-treated rats was essentially unaffected by pretreatment of the rats with puromycin or cycloheximide, but was abolished by pretreatment of the cytosols in vitro with alpha-mannosidase or beta-galactosidase. Passage of cytosols of control and experimental livers through concanavalin A-agarose columns concentrated the activities of the eluates in stimulating in vitro labeled nuclear RNA release. In vivo 14C-orotate labeling of hepatic nuclear RNA for 30 minutes was increased by hypertonic NaCl treatment in comparison with water treatment of control animals. In vivo 14C-glucosamine incorporation into hepatic proteins of nuclei and nuclear envelopes was increased in hypertonic NaCl-treated rats in comparison with controls. In vitro 3H-tryptophan binding to proteins (trichloracetic acid-precipitable) to cytosols of livers of hypertonic NaCl-treated rats was increased in comparison with binding of controls. The results suggest that the administration of hypertonic NaCl rapidly leads to a change in hepatic cytosol whereby the activity to stimulate in vitro labeled nuclear RNA release is enhanced. This occurs without new protein synthesis, and the effect is probably mediated through a glycoprotein. In contrast, the hepatic nuclei of the rats treated with hypertonic NaCl show a decreased ability to release in vitro labeled nuclear RNA, possibly because of the development of a nuclear lesion.

Effects of varying fat content of a high tryptophan diet on the induction of gamma-glutamyltranspeptidase positive foci in the livers of rats treated with hepatocarcinogen

The influence of varying the dietary fat content on the emergence of gamma-glutamyltranspeptidase (GGT)-positive foci in the livers of male rats fed elevated (2%) L-tryptophan (TRP) and exposed to a hepatocarcinogen was investigated. Subtotal hepatectomies were performed, and 18 h later the rats were treated with diethylnitrosamine (DEN) (30 mg/kg). Ten days later 4 dietary groups were followed for 10 weeks: (1) control diet containing 15% fat (C-HF); (2) control diet containing 5% fat (C-LF); (3) C-HF + TRP; (4) C-LF + TRP. Rats fed elevated TRP diets (C-HF + TRP and C-LF + TRP) similarly developed more and larger GGT+ foci than did rats fed the regular TRP diets (C-HF and C-LF), indicating that the promotional effect of elevated dietary TRP was not affected by the fat level (15% vs. 5%).

Evidence for the role of glycosylation of proteins in the tryptophan-induced stimulation of nucleocytoplasmic translocation of mRNA in rat liver

Tryptophan induces a rapid stimulation of polyribosomal aggregation and protein synthesis in the livers of rats or mice. This stimulatory effect of tryptophan correlates with increased levels of mRNA in the cytoplasm of the liver and is related to enhanced translocation of nuclear mRNA into the cytoplasm. In the present study the possible role of glycoproteins of the rat liver, particularly those in the nuclear membranes and in the cytosol, in relation to the effect of tryptophan on enhanced nucleocytoplasmic translocation of mRNA was investigated. In the standard treatment regimen, tryptophan (30 mg/100 gm of body weight) was administered by stomach tube 10 minutes before killing. The following results were noted in the liver: Administration of tryptophan increased [14C]glucosamine incorporation into proteins of the subcellular fractions, particularly those of the soluble, nucleus and nuclear membrane. In vivo treatment of rats with tryptophan increased the in vitro [14C]orotate-labeled nuclear RNA release and [3H]tryptophan binding to proteins of the nuclei or cytosols. Treatment of cytosol proteins with alpha-mannosidase or beta-galactosidase, but not with neuraminidase, inhibited these increases. After treatment of cytosol fractions on a concanavalin A agarose column, the effluents showed decreased activity and the eluates showed increased activity in in vitro nuclear RNA release and in tryptophan binding to proteins of the control and, particularly, of the tryptophan-treated animals. Administration of tryptophan increased the polyribosomal aggregation, the in vitro [14C]leucine incorporation into protein, and the in vitro nuclear RNA release by cytosol. However, tunicamycin pretreatment of rats prevented these increases due to tryptophan. The data of this study suggest that glycosylated proteins, one or more, are the active components whereby tryptophan acts upon the liver.

Protective effect of tryptophan and cysteine against carbon tetrachloride-induced liver injury

The effects of the administration of tryptophan and/or cysteine on carbon tetrachloride (CCl4)-induced hepatic injury were investigated. Rats received CCl4 (1 ml/kg ip) followed 6 hr later by tryptophan (300 mg/kg) and/or cysteine (950 mg/kg) via stomach tube and rats were killed after 24 hr. Treatment with tryptophan, cysteine, or both reduced the degree of hepatic necrosis observed histologically. While CCl4 caused polyribosomal disaggregation and decreased [14C]leucine incorporation into liver proteins in vitro and in vivo, treatment with tryptophan, cysteine, or both caused a shift in polyribosomes toward heavier aggregation and protein synthesis was increased. Serum activities of lactic dehydrogenase (LDH), glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, and gamma-glutamyl-transpeptidase were markedly increased after CCl4 alone but after subsequent treatment with cysteine or with tryptophan and cysteine appreciable decreases occurred. Glutathione concentration decreased but total amount remained constant in the livers of CCl4-treated rats while subsequent treatment with cysteine alone or together with tryptophan elevated both levels of glutathione. Using isolated hepatocytes, CCl4 caused decreases in cell viability, in release of LDH, and in [14C]leucine incorporation into protein. Treatment with CCl4 and tryptophan and/or cysteine revealed that cysteine alone or with tryptophan improved cell viability and decreased LDH release of the cells, while tryptophan alone or with cysteine improved protein synthesis. Upon cytologic evaluation, the isolated hepatocytes revealed membrane distortions after CCl4 alone but these were less marked after CCl4 plus tryptophan, cysteine, or both (most improvement). Thus, tryptophan and cysteine act in a beneficial manner against CCl4-induced hepatic injury in the rat.

Influence of dietary tryptophan on the induction of gamma-glutamyltranspeptidase-positive foci in the livers of rats treated with hepatocarcinogen

The ingestion of an elevated level (2%) of L-tryptophan (TRP) in a purified diet was investigated to determine whether it would influence the induction of gamma-glutamyltranspeptidase (GGT)-positive foci in the livers of rats exposed to a hepatocarcinogen. Subtotal hepatectomies were performed, and 18 h later, the rats were given injections i.p. of diethylnitrosamine (30 mg/kg). Ten days later, groups of male rats were placed on choline-supplemented (CS), CS + TRP, choline-deficient (CD), or CD + TRP diets for 10 wk. In two separate experiments, the rats fed the CS + TRP diet or the CD diet developed more and larger GGT + foci than did rats fed the CS diet. Rats fed the CD + TRP diet revealed similar changes to those found in rats fed the CD diet. The liver weights of the rats fed the CD or the CD + TRP diet were greater than those of rats fed the CS or the CS + TRP diet. Hepatic GGT activity was somewhat elevated in rats fed the CS + TRP diet and markedly elevated in rats fed the CD or the CD + TRP diet. Hepatic ornithine decarboxylase activity was increased in rats fed the CD + TRP diet. The results suggest that increased dietary tryptophan has a promoting effect on liver carcinogenesis as measured by the induction of GGT + foci in the livers of rats exposed to diethylnitrosamine. A potentiating effect by tryptophan was not observed in the livers of rats fed a CD diet.

Hepatic ornithine decarboxylase activity in the rat as influenced by retinyl acetate and ethanol or tryptophan

Ethanol and tryptophan have been demonstrated earlier to induce a rapid stimulation of hepatic ornithine decarboxylase (ODC) activity in overnight-fasted rats. In this study the effect of the administration of retinyl acetate prior to administering ethanol or tryptophan 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. Intraperitoneal administration of retinyl acetate (1 microgram/100 g body wt) 1 hr before tube feeding ethanol (0.75 g as a 50% solution/100 g body wt) or L-tryptophan (30 mg in 3 ml water/100 g body wt) and 3 hr before killing caused an enhanced stimulation of hepatic ODC activity compared to that when each agent was administered alone. In vitro [14C]leucine incorporation into protein using hepatic microsomes of tryptophan-treated rats with or without retinyl acetate was increased in comparison with that of controls while decreases were observed when using microsomes of ethanol-treated rats with or without retinyl acetate. Although retinyl acetate has been reported earlier to inhibit the stimulation of hepatic ODC activity due to a variety of agents, including some agents known as carcinogens or promoters, it did not act in this manner against the acute administration of ethanol or tryptophan.

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.

Effect of tryptophan on informosomal and polyribosome-associated messenger RNA in rat liver

The possible role that informosomal mRNA may play in the stimulation of hepatic protein synthesis induced by the acute administration of tryptophan was investigated. L-tryptophan (30 mg/100 g body weight) tube-fed to rats induced an increase (20%) in the amount of polyribosome-associated poly(A+)mRNA in the liver within 1 hour. On the other hand, the amount of the informosomal poly(A+)- mRNA revealed no significant increase or decrease. The size of the increase in the polyribosome-associated poly(A+)mRNA pool was equal to the entire amount of informosomal poly(A+)mRNA present in the hepatic cells. Therefore it was concluded that the failure to detect a significant decrease in the size of the informosomal mRNA pool indicated that the increase in the polyribosome-associated poly(A+)mRNA must be due to a different mechanism, such as enhanced nuclear-to-cytoplasmic translocation of nuclear poly(A+)mRNA, which had been reported earlier. To determine whether any qualitative or quantitative changes occurred in the RNA sequences along with the increase in poly(A+)mRNA following tryptophan administration, DNA/RNA hybridization studies were conducted by using hepatic polyribosome-associated poly(A+)- mRNA from tryptophan-treated and control rats. Although qualitatively no new species of mRNA were detected in the mRNA from tryptophan-treated rats, kinetic analysis of the hybridization curves indicated that there was a shift or accumulation of hepatic poly(A+)mRNA belonging to the intermediate and possibly the high frequency classes of polyribosome-associated poly(A+)mRNA in the livers of the tryptophan-treated rats.

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.

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.

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.

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.