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PubMed1991

Tryptophan mutants in Arabidopsis: the consequences of duplicated tryptophan synthase beta genes.

The cruciferous plant Arabidopsis thaliana has two closely related, nonallelic tryptophan synthase beta genes (TSB1 and TSB2), each containing four introns and a chloroplast leader sequence. Both genes are transcribed, although TSB1 produces greater than 90% of tryptophan synthase beta mRNA in leaf tissue. A tryptophan-requiring mutant, trp2-1, has been identified that has about 10% of the wild-type tryptophan synthase beta activity. The trp2-1 mutation is complemented by the TSB1 transgene and is linked genetically to a polymorphism in the TSB1 gene, strongly suggesting that trp2-1 is a mutation in TSB1. The trp2-1 mutants are conditional: they require tryptophan for growth under standard illumination but not under very low light conditions. Presumably, under low light the poorly expressed gene, TSB2, is capable of supporting growth. Genetic redundancy may be common to many aromatic amino acid biosynthetic enzymes in plants because mutants defective in two other genes (TRP1 and TRP3) also exhibit a conditional tryptophan auxotrophy. The existence of two tryptophan pathways has important consequences for tissue-specific regulation of amino acid and secondary metabolite biosynthesis.

Amino Acid Sequence↗

PubMed1981

The mechanism of tryptophan binding to tryptophan synthase from Escherichia coli.

The kinetics of the binding of L-tryptophan to the alpha 2 holo beta 2 complex of tryptophan synthase from Escherichia coli have been measured by rapid-mixing techniques under conditions where tryptophan release is mainly rate-determining in tryptophan synthesis. The dependence of the three observable rate processes on the concentration of L-tryptophan suggests a mechanism in which a rapid binding step is followed by two isomerizations. The effect of the substrate analogue indolepropanol phosphate on the kinetics of binding and synthesis from L-serine and indole supports a branched mechanism with an unproductive enzyme-ligand complex being the major species. The productive enzyme-ligand complex absorbs light at 473 nm but not at 500 nm. These observations, and binding studies with D-tryptophan, suggest that at least two alterative modes of binding of L-tryptophan exist on the enzyme. The effects of protons, indole and indolepropanol phosphate on the three rate processes explain the dependence of kcat on the three non-competitive ligands.

Benzimidazoles↗

PubMed2005

Somatodendritic autoreceptor regulation of serotonergic neurons: dependence on L-tryptophan and tryptophan hydroxylase-activating kinases.

The somatodendritic 5-HT(1A) autoreceptor has been considered a major determinant of the output of the serotonin (5-HT) neuronal system. However, recent studies in brain slices from the dorsal raphe nucleus have questioned the relevance of 5-HT autoinhibition under physiological conditions. In the present study, we found that the difficulty in demonstrating 5-HT tonic autoinhibition in slice results from in vitro conditions that are unfavorable for sustaining 5-HT synthesis. Robust, tonic 5-HT(1A) autoinhibition can be restored by reinstating in vivo 5-HT synthesizing conditions with the initial 5-HT precursor l-tryptophan and the tryptophan hydroxylase co-factor tetrahydrobiopterin (BH(4)). The presence of tonic autoinhibition under these conditions was revealed by the disinhibitory effect of a low concentration of the 5-HT(1A) antagonist WAY 100635. Neurons showing an autoinhibitory response to L-tryptophan were confirmed immunohistochemically to be serotonergic. Once conditions for tonic autoinhibition had been established in raphe slice, we were able to show that 5-HT autoinhibition is critically regulated by the tryptophan hydroxylase-activating kinases calcium/calmodulin protein kinase II (CaMKII) and protein kinase A (PKA). In addition, at physiological concentrations of L-tryptophan, there was an augmentation of 5-HT(1A) receptor-mediated autoinhibition when the firing of 5-HT cells activated with increasing concentrations of the alpha(1) adrenoceptor agonist phenylephrine. Increased calcium influx at higher firing rates, by activating tryptophan hydroxylase via CaMKII and PKA, can work together with tryptophan to enhance negative feedback control of the output of the serotonergic system.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1984

High doses of vitamin B6 in the rat are associated with inhibition of hepatic tryptophan metabolism and increased uptake of tryptophan into the brain.

Acute administration of vitamin B6 to rats (10 mg/kg body weight) led to reduced urinary excretion of N1-methyl nicotinamide and methyl pyridone carboxamide, indicating inhibition of the oxidative metabolism of tryptophan. There was a considerable reduction in the production of 14CO2 from [ring-2-14C]tryptophan, and a significant inhibition of hepatic tryptophan oxygenase when measured in liver homogenates, together with an increase in the concentration of tryptophan in plasma. There was an increase in both the concentration of tryptophan in the brain and the uptake into the brain of peripherally administered [3H]tryptophan, accompanied by a small increase in the rate of synthesis of 5-hydroxytryptamine in the brain. It is suggested that this increase in the uptake of tryptophan into the brain following a relatively large dose of vitamin B6 may explain the beneficial action of the vitamin in some cases of depressive illness.

Animals↗

PubMed1983

Effect of streptozotocin-induced diabetes on tryptophan oxygenase activity and brain tryptophan levels in rats.

Alterations in brain tryptophan levels and the rate of hepatic tryptophan metabolism by tryptophan oxygenase (TPO) were studied in male Sprague-Dawley rats rendered diabetic by intravenous administration of streptozotocin (STZ), 65 mg/kg. Determinations were made at the early onset of diabetes (1-4 days of glucosuria) and 8-12 days following STZ injection. Rats were considered diabetic if their serum glucose exceeded 250 mg percent. Tryptophan brain levels decreased by 17% after four days of diabetes, decreased by 22% on day 5, and by 27% 8-12 days after STZ. Brain 5-hydroxyindoleacetic acid levels were significantly decreased by 27% on day 5, but returned to control levels by 8-12 days. Serotonin concentration in the brain remained at control values. The initial appearance of a significant increase in total TPO activity coincided with the onset of a change in brain tryptophan. Total TPO activity increased by 60% after 4 days of diabetes. The increase was caused by an increase in apoenzyme activity since holoenzyme activity remained unaltered. Holoenzyme activity was increased by 37% after 8-12 days, and accounted for the change in total TPO activity. Insulin treatment reversed the STZ-induced alterations. The results are compatible with the hypothesis that diabetes increases hepatic TPO activity that in turn results in decreased plasma tryptophan levels and decreased availability of tryptophan for brain uptake. However, compensatory changes appear to maintain a stable serotonin concentration in the brain. The early and later changes in TPO activity during diabetes are apparently caused by different regulatory events.

Animals↗

PubMed1996

The tryptophan content in protein of cereal grains and legume seeds as a function of nitrogen content. A reappraisal of tryptophan score.

UNLABELLED: The tryptophan content ([Trp]) in the dry matter (DM) of wheat, maize, barley, sorghum, rice, pearl millet grains, pea and broad bean seeds is evaluated from samples, with various nitrogen contents ([N]DM) and genotypes, using a procedure that has been shown to be strictly quantitative. The determination of linear correlations between [Trp]DM and [N]DM, and between the tryptophan content in protein ([Trp]N) and [N]DM or 1/[N]DM for every species leads to the following observations: (1) [Trp]DM and [N]DM are linearly related. The data show that previous reports of similar relationships underestimate tryptophan by 10 +/- 5% owing to tryptophan degradation during alkaline hydrolysis preparatory to analysis; (2) the linear correlations between [Trp]N and 1/[N]DM, resulting from linear relationships [Trp]DM and [N]DM display coefficients of determination (r2) far lower than 1 and similar to those found for linear correlations between [Trp]N and [N]DM; (3) [Trp]N increases with [N]DM increasing for rice and pearl millet while it decreases for all other species. IN CONCLUSION: (1) linear relationships between tryptophan and nitrogen have a low predictive value; (2) the nutritional score of tryptophan of foods and feeds, as calculated from the determination of tryptophan using a procedure involving alkaline hydrolysis, is generally underestimated by 10%.

Edible Grain↗

PubMed2000

The relative importance of tryptophan-dependent and tryptophan-independent biosynthesis of indole-3-acetic acid in tobacco during vegetative growth.

A quantitative study of indole-3-acetic acid (IAA) turnover, and the contribution of tryptophan-dependent and tryptophan-independent IAA-biosynthesis pathways, was carried out using protoplast preparations and shoot apices obtained from wild-type and transgenic, IAA-overproducing tobacco (Nicotiana tabacum L.) plants, during a phase of growth when the level of endogenous IAA was stable. Based on the rate of disappearance of [13C6]IAA, the half-life of the IAA pool was calculated to be 1.1 h in wild-type protoplasts and 0.8 h in protoplasts from the IAA-overproducing line, corresponding to metabolic rates of 59 and 160 pg IAA (microg Chl)(-1) h(-1), respectively. The rate of conversion of tryptophan to IAA was 15 pg IAA (microg Chl)(-1) h(-1) in wild-type protoplasts and 101 pg IAA (microg Chl)(-1) h(-1) in protoplasts from IAA-overproducing plants. In both instances, IAA was metabolised more rapidly than it was synthesised from tryptophan. As the endogenous IAA pools were in a steady state, these findings indicate that IAA biosynthesis via the tryptophan-independent pathway was 44 pg IAA (microg Chl)(-1) h(-1) and 59 pg IAA (microg Chl)(-1) h(-1), respectively, in the wild-type and transformed protoplast preparations. In a parallel study with apical shoot tissue, the presumed site of IAA biosynthesis, the rate of tryptophan-dependent IAA biosynthesis exceeded the rate of metabolism of [13C6]IAA despite the steady state of the endogenous IAA pool. The most likely explanation for this anomaly is that, unlike the protoplast system, injection of substrates into the apical tissues did not result in uniform distribution of label, and that at least some of the [2H5]tryptophan was metabolised in compartments not normally active in IAA biosynthesis. This demonstrates the importance of using experimental systems where labelling of the precursor pool can be strictly controlled.

Carbon Isotopes↗

PubMed1990

Tryptophan-130 is the most reactive tryptophan residue in rabbit skeletal myosin subfragment-1.

Rabbit skeletal muscle myosin subfragment-1 (S-1) was reacted with dimethyl(2-hydroxy-5-nitrobenzyl)sulfonium bromide (DHNBS) resulting in modification of 0.8 tryptophan residues per S-1. In order to assign the most reactive tryptophan of the 5 S-1 tryptophans, antibodies were raised in rabbits against bovine serum albumin modified with DHNBS. The antibodies reacted with the 27 kDa tryptic fragment of DHNBS-treated S-1, indicating that the reactive tryptophan resides on this domain. The 27 kDa fragment was isolated from DHNBS-treated S-1 and was further cleaved at a single cysteine residue by 2-nitro-5-thiocyanobenzoic acid. This cleavage resulted in two peptides, each of them containing one tryptophan. The antibodies reacted with the smaller peptide consisting of residues 122-204. The only tryptophan residing on this peptide is Trp130, and this is therefore the most reactive tryptophan of S-1.

Animals↗

PubMed1980

Relationship between plasma ratio of tryptophan to competing amino acids and the response to L-tryptophan treatment in endogenously depressed patients.

The ratio of the plasma of total tryptophan to those amino acids that compete with tryptophan during transport into the brain was determined in 60 control subjects and 87 patients suffering from endogenous depression, all females. The plasma ratio in the control subjects showed a significant negative correlation with age. There was no significant difference in the distribution of the biochemical data between the control subjects and the depressed patients. There was a significant higher proportion of bipolar depressed subjects compared to unipolar depressives and patients of uncertain polarity who showed a plasma ratio in the lower normal range. Thirty-two patients were subsequently treated with L-tryptophan. In the patients who showed a particularly low plasma ratio of tryptophan to competing amino acids a remission frequency of 80% was observed on day 14. The efficacy of L-tryptophan in the patients who showed a plasma ratio within the upper normal range was extremely poor. The results suggest that the ratio in the plasma of tryptophan to competing amino acids is a useful predictor of the course of treatment of depressed subjects with L-tryptophan.

Adult↗

PubMed1990

Resolution of the fluorescence decay of the two tryptophan residues of lac repressor using single tryptophan mutants.

We have studied the time-resolved intrinsic tryptophan fluorescence of the lac repressor (a symmetric tetramer containing two tryptophan residues per monomer) and two single-tryptophan mutant repressors obtained by site-directed mutagenesis, lac W201Y and lac W220Y. These mutant repressor proteins have tyrosine substituted for tryptophan at positions 201 and 220, respectively, leaving a single tryptophan residue per monomeric subunit at position 220 for the W201Y mutant and at position 201 in the W220Y mutant. It was found that the two decay rates recovered from the analysis of the wild type data do not correspond to the rates recovered from the analysis of the decays of the mutant proteins. Each of these residues in the mutant repressors displays at least two decay rates. Global analysis of the multiwavelength data from all three proteins, however, yielded results consistent with the fluorescence decay of the wild type lac repressor corresponding simply to the weighted linear combination of the decays from the mutant proteins. The effect of ligation by the antagonistic ligands, inducer and operator DNA, was similar for all three proteins. The binding of the inducer sugar resulted in a quenching of the long-lived species, while binding by the operator decreased the lifetime of the short components. Investigation of the time-resolved anisotropy of the intrinsic tryptophan fluorescence in these three proteins revealed that the depolarization of fluorescence resulted from a fast motion and the global tumbling of the macromolecule. Results from the simultaneous global analysis of the frequency domain data sets from the three proteins revealed anisotropic rotations for the macromolecule, consistent with the known elongated shape of the repressor tetramer. In addition, it appears that the excited-state dipole of tryptophan 220 is alighed with the long axis of the repressor.

Ligands↗

PubMed1998

Single-tryptophan mutants of monomeric tryptophan repressor: optical spectroscopy reveals nonnative structure in a model for an early folding intermediate.

A monomeric version of the dimeric tryptophan repressor from Escherichia coli, L39E TR, has previously been shown to resemble a transient intermediate that appears in the first few milliseconds of folding [Shao, X., Hensley, P., and Matthews, C. R. (1997) Biochemistry 36, 9941-9949]. In the present study, the optical properties of the two intrinsic tryptophans were used to compare the structure and dynamics of the monomeric form with those of the native, dimeric form. The urea-induced unfolding equilibria of Trp19/L39E TR (Trp99 replaced with Phe) and Trp99/L39E TR (Trp19 replaced with Phe) mutants were monitored by circular dichroism and fluorescence spectroscopies at pH 7.6 and 25 degrees C. Coincident normalized transitions show that the urea denaturation process for each single-tryptophan mutant follows a two-state model involving monomeric native and unfolded forms. The free energies at standard state in the absence of denaturant for Trp19/L39E TR and Trp99/L39E TR are less than that for L39E TR, indicating that both tryptophans are involved in stabilizing the monomer. Fluorescence and near-UV circular dichroism spectroscopies indicate that the tryptophan side chains in monomeric Trp19/L39E TR and Trp99/L39E TR occupy hydrophobic, well-structured environments that are distinctively different from those found in their dimeric counterparts. Acrylamide quenching experiments show that both Trp19 and Trp99 are partially exposed to solvent in the native state, with Trp99 having a slightly greater degree of exposure. Measurements of the steady-state anisotropies of Trp19/L39E and Trp99/L39E TR demonstrate that the motions of both tryptophan side chains are restricted in the folded conformation. On the basis of these data, it can be concluded that this monomeric form of the tryptophan repressor adopts a well-folded, stable conformation with nonnative tertiary structure. When combined with previous results, the current findings demonstrate that the development of higher order structure during the folding of this intertwined dimer does not follow a simple hierarchical model.

Bacterial Proteins↗

PubMed2004

Detection of tryptophan to tryptophan energy transfer in proteins.

Förster resonance energy transfer (FRET) studies usually involve observation of intensity or lifetime changes in the donor or acceptor molecule and usually these donor and acceptor molecules differ (heterotransfer). The use of polarization to monitor FRET is far less common, although it was one of the first methods utilized. In 1960, Weber demonstrated that homotransfer between tryptophan molecules contributes to depolarization. He also discovered that the efficiency of homotransfer becomes much less effective upon excitation near the red-edge of the absorption. This "red-edge effect" was shown to be a general phenomenon of homotransfer. We have utilized Weber's red-edge effect to study tryptophan homotransfer in proteins. Specifically, we determined the polarization of the tryptophan fluorescence upon excitation at 295 nm and 310 nm (near the red-edge). Rotational diffusion leads to depolarization of the emission excited at either 295 nm or 310 nm, but homotransfer only contributes to depolarization upon excitation at 295 nm. Hence, the 310/295 polarization ratio gives an indication of tryptophan to tryptophan energy transfer. In single tryptophan systems, the 310/295 ratios are generally below 2 whereas in multi-tryptophan systems, the 310/295 ratios can be greater than 3.

Animals↗

PubMed1980

Excretion of tryptophan-niacin metabolites by young men: effects of tryptophan, leucine, and vitamin B6 intakes.

Three human metabolic studies, each 35 days in length, were performed to investigate the relationship between tryptophan intake and the proportion of dietary tryptophan converted to niacin and the effect of supplements of L-leucine and vitamin B6 on this conversion. Nine college men consumed a basal diet that provided 8 mg of niacin, 1 mg of vitamin B6, and either 245, 548, or 845 mg of tryptophan from proteins per day. During each 35-day study, for one 15-day period basal diet alone was consumed, for another 15-day period basal diet plus 10 g of L-leucine per day was consumed, and for the last 5-day period, 20 mg of vitamin B6 per day was added to the diets of both groups. N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and quinolinic acid were measured in 24-hr urine samples. There were no significant or consistent effects of L-leucine or vitamin B6 supplements on the excretin of any of the metabolites measured. The proportion of tryptophan converted to niacin tended to increase as tryptophan consumption increased; however, this change was small and was probably not significant over the range of tryptophan intakes studied. The average conversion ration of tryptophan to niacin was approximately 72:1 in these subjects.

Adult↗

PubMed1990

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.

Alanine↗

PubMed2000

Functional analysis of a tryptophan-less P-glycoprotein: a tool for tryptophan insertion and fluorescence spectroscopy.

P-glycoprotein (Pgp) functions as an ATP-dependent drug efflux pump to confer multidrug resistance to tumor cells. In the absence of a high-resolution structure for this protein, several important and intriguing aspects of Pgp structure and function remain poorly understood. Fluorescence spectroscopy of endogenous or genetically engineered tryptophan residues represents a potentially powerful method to probe static and dynamic aspects of Pgp at high resolution. We have used site-directed mutagenesis to modify the wild-type (WT) mouse mdr3 Pgp for tryptophan fluorescence spectroscopy by replacement of all 11 tryptophan residues individually with phenylalanine. None of the 11 tryptophans were found to be absolutely essential for Pgp activity, because Chinese hamster ovary cells transfected and overexpressing this mutant Trp-less mdr3 cDNA (mdr3F(1-11)) become multidrug-resistant and can carry out active transport of vinblastine, colchicine, and Calcein-AM. The mdr3F(1-11) mutant has reduced activity compared with WT Mdr3, and shows a unique pattern of drug resistance clearly distinct from WT and, as opposed to the latter, can neither confer FK-506 resistance nor functionally complement ste6 in yeast. Studies with Pgp mutants containing either single or double tryptophan residues or with chimeric molecules constructed between wild-type Pgp and mdr3F(1-11) indicated that no single tryptophan residue was responsible for the reduced activity of the mdr3F(1-11) mutant. Likewise, all but one chimeric Pgp preserved the unique drug resistance profile of the mdr3F(1-11) mutant. Altogether, we show that a Trp-less Pgp is functionally active and can be used as a molecular backbone for insertion of tryptophans in strategic locations to probe various aspects of Pgp function.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed1970

Metabolism of tryptophan by Pseudomonas aureofaciens. 3. Production of substituted pyrrolnitrins from tryptophan analogues.

Exogenous tryptophan is metabolized by Pseudomonas aureofaciens to yield pyrrolnitrin [3-chloro-4-(2'-nitro-3'-chlorophenyl)-pyrrole], an antifungal agent. The ability of this culture to metabolize tryptophan analogues in a similar manner was investigated by addition of the appropriate compound to the fermentation. Tryptophan precursors and metabolites or nonphenyl-substituted tryptophans had little effect on pyrrolnitrin biosynthesis, but simple derivatives of indole inhibited the production of pyrrolnitrin. Tryptophans substituted at the 4 position decreased pyrrolnitrin production and were converted into the corresponding substituted indoles. Tryptophans substituted at the 5, 6, and 7 position with fluorine or at the 5 and 7 position with methyl yielded new pyrrolnitrin derivatives. Substitution of larger groups (such as chloro, bromo, trifluoromethyl, and methoxy) at these positions led to the formation of the intermediate, amino pyrrolnitrin [3-chloro-4-(2'-amino-3'-chlorophenyl)-pyrrole], with the appropriate new substituent. The trifluoromethyl group at the 6 position of tryptophan prevented chlorination at the 3 position of pyrrolnitrin.

Antifungal Agents↗

PubMed1970

Tryptophan transport in Neurospora crassa: a tryptophan-binding protein released by cold osmotic shock.

Osmotic shock treatment of germinated conidia of Neurospora reduced the capacity for tryptophan transport in these cells approximately 90% without an appreciable loss of cell viability. Tryptophan-binding proteins and alkaline phosphatase were consistently released into the osmotic shock fluid by this treatment. Four lines of evidence suggest that the binding protein may be related to the tryptophan transport system. (i) It appears to be located on or near the cell surface. (ii) a decreased capacity for binding tryptophan was observed in shock fluids from cells repressed for tryptophan uptake; reduced or altered binding capacity was released from a transport-negative mutant. (iii) The specificity of tryptophan binding was similar to that observed in the in vivo transport system. (iv) The dissociation constant for binding, as measured by equilibrium dialysis, was approximately the same as the K(m) for tryptophan transport.

Alkaline Phosphatase↗

PubMed2000

Acute effects of L-tryptophan on tryptophan hydroxylation rate in brain regions (hypothalamus and medulla) of rainbow trout (Oncorhynchus mykiss).

Levels of 5-hydroxytryptophan (5-HTP) in brain regions (hypopthalamus and medulla) of rainbow trout were analysed by HPLC-EC 0, 10, 30, and 40 min after intraperitoneal administration of different doses of L-tryptophan (Trp) (0, 12.5, and 25 mg. kg(-1) body weight) in fish treated with 3-hydroxybenzylhydrazine (NSD1015; 75 mg. kg(-1)). The results show that, in control fish, 5-HTP levels in hypothalamus (58.03 +/- 6.36 pg. mg(-1) brain tissue) were significantly higher than those observed in medulla (28.04 +/- 4.32 pg. mg(-1) brain tissue). Basal tryptophan hydroxylation rates (after 0 mg. kg(-1) Trp administration) were 0.42 +/- 0.07 pg 5-HTP. mg(-1). min(-1), and 0.63 +/- 0.24 pg 5HTP. mg(-1). min(-1), for hypothalamus and medulla respectively. On the other hand, the results demonstrate that L-tryptophan administration induced significant increases in the rate of tryptophan hydroxylation, both in hypothalamus and medulla. These findings indicate that, in a way similar to that observed in mammals, brain tryptophan hydroxylase is unsaturated by its substrate (tryptophan) under normal physiological conditions. J. Exp. Zool. 286:131-135, 2000.

5-Hydroxytryptophan↗