Considerations of Mechanisms Involved

A number of reports have demonstrated that L-tryptophan has a regulatory effect at the posttranscriptional level of hepatic protein synthesis. Details 

To determine whether the rapidly stimulated hepatic protein synthesis following L-tryptophan administration was involved in this process, pretreatment of the animals with inhibitors of protein synthesis was followed for their influence on the increased transporting effect of the liver cell sap of L-tryptophan-treated rats. Animals were pretreated with cycloheximide for 2.5 h or with puromycin for 20 min before the L-tryptophan or water administration, which was given 10 min before killing. The effects of liver saps prepared from the control and experimental groups on in vitro release of labeled RNA from hepatic nuclei were investigated. Liver cell saps from rats treated with cycloheximide or puromycin before L-tryptophan administration were not able to stimulate the release of labeled RNA, as could liver cell saps of L-tryptophan-treated rats.102 

Summarizing the above findings, it appears that the enhanced nucleocy-toplasmic translocation of mRNA in the livers of L-tryptophan-treated animals affects both the nucleus and the cytosol. The nuclear effect appears to be independent of changes in hepatic protein synthesis, while the cytosol effect is dependent on hepatic protein synthesis. Thus, while both (nuclear 

Activities of two other enzymes, protein phosphokinease and phospho-protein phosphohydrolase, have also been identified on the mammalian nuclear envelope.113-115 It has been suggested that the levels of phosphorylation and dephosphorylation of the nuclear envelope protein by these two enzymes may regulate nucleocytoplasmic RNA translocation.116 Because these nuclear envelope-associated enzymes may play a key role in the regulation of nuclear RNA transport, a study was conducted to investigate whether the administration of tryptophan would influence the phosphorylation and dephosphorylation process in the hepatic nuclear envelopes, which may then modulate nucleocytoplasmic transport of RNA. The activ- 

Since L-tryptophan administration rapidly enhanced nucleocytoplasmic translocation of RNA in the liver, it was of interest to learn whether tryptophan deprivation would be inhibitory to this process. A few experimental studies suggested that indeed this was the case. Bocker et al.,121 using rats 

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