Tryptophan binding to nuclei of rat brain

L-Tryptophan: Biochemical, nutritional and pharmacological aspects

Tryptophan is important both for protein synthesis and as a precursor of niacin, serotonin and other metabolites. Tryptophan is an unusual amino acid because of the complexity of its metabolism, the variety and importance of its metabolites, the number and diversity of the diseases it is involved in, and because of its use in purified form as a pharmacological agent. This review covers the metabolism of tryptophan, its presence in the diet, the disorders associated with low tryptophan levels due to low dietary intake, malabsorption, or high rates of metabolism, the therapeutic effects of tryptophan and the side effects of tryptophan when it is used as a drug including eosinophilia myalgia syndrome.

Acute tryptophan depletion in humans: a review of theoretical, practical and ethical aspects

The acute tryptophan depletion (ATD) technique has been used extensively to study the effect of low serotonin in the human brain. This review assesses the validity of a number of published criticisms of the technique and a number of previously unpublished potential criticisms. The conclusion is that ATD can provide useful information when results are assessed in conjunction with results obtained using other techniques. The best-established conclusion is that low serotonin function after tryptophan depletion lowers mood in some people. However, this does not mean that other variables, altered after tryptophan depletion, are necessarily related to low serotonin. Each aspect of brain function has to be assessed separately. Furthermore, a negative tryptophan depletion study does not mean that low serotonin cannot influence the variable studied. This review suggests gaps in knowledge that need to be filled and guidelines for carrying out ATD studies.

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.

Inflammation-associated changes in the cellular availability of tryptophan and kynurenine in renal transplant recipients

In the course of evaluating the hypothesis that tryptophan or tryptophan metabolites mediate some of the physiological or pathological aspects of the inflammatory response, we assessed the bioavailability of tryptophan and kynurenine in renal allograft recipients during periods of stable graft function, acute rejection and OKT3 therapy. In normal controls and patients with stable function, approximately 8% of the tryptophan and less than 5% of the kynurenine in serum were present in the freely diffusable form. The free tryptophan concentration was significantly increased during acute rejection, while free tryptophan as well as total and free kynurenine concentrations were significantly increased during OKT3 therapy. In each case the ratio of free indole to the sum of the plasma concentrations of large neutral amino acids was also increased. In vitro studies of indole binding to human serum proteins demonstrated the parallel displacement of bound tryptophan and kynurenine by physiological changes in pH, serum albumin concentration and free fatty acid concentration. The results suggest that inflammation associated increases in the oxidative metabolism of tryptophan are accompanied by the increased availability of serum indoles for intracellular metabolism in the tissues.

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.