Kainate receptor-mediated synaptic currents in mudpuppy inner retinal neurons reduced by D-O-phosphoserine

1. The effects of D-O-phosphoserine (DOS) were examined on proximal neurons in the superfused mudpuppy retinal-eyecup preparation by measuring their synaptically evoked whole-cell currents with the use of patch-clamp electrodes. 2. DOS reduced the light-evoked excitatory postsynaptic potentials (EPSPs) of amacrine and ganglion cells. This suppression was present even though the center responses of both ON- and OFF-bipolar cells were unaffected by DOS. 3. When recordings were done under voltage-clamp conditions. DOS diminished the magnitude of light-evoked synaptic currents associated with a reduction in synaptic conductance. 4. To determine which acidic amino acid receptor mediated the network-selective action of DOS, various glutamate agonists were tested against this excitatory amino acid receptor (EAAR) antagonist. DOS blocked the depolarizing effects of kainate (KA), but not those of N-methyl-D-aspartate (NMDA) or quisqualate (QQ). Thus DOS was a selective KA antagonist, and KA receptors appear to be the dominant EAAR subtype that mediates synaptic inputs into the inner retina of the mudpuppy.

Phospholamban phosphorylation in intact ventricles. Phosphorylation of serine 16 and threonine 17 in response to beta-adrenergic stimulation

Phospholamban is the major membrane protein of the heart phosphorylated in response to beta-adrenergic stimulation. In cell-free systems, cAMP-dependent protein kinase catalyzes exclusive phosphorylation of serine 16 of phospholamban, whereas Ca2+/calmodulin-dependent protein kinase gives exclusive phosphorylation of threonine 17 (Simmerman, H. K. B., Collins, J. H., Theibert, J. L., Wegener, A. D., and Jones, L. R. (1986) J. Biol. Chem. 261, 13333-13341). In this work we have localized the sites of phospholamban phosphorylation in intact ventricles treated with the beta-adrenergic agonist isoproterenol. Isolation of phosphorylated phospholamban from 32P-perfused guinea pig ventricles, followed by partial acid hydrolysis and phosphoamino acid analysis, revealed phosphorylation of both serine and threonine residues. At steady state after isoproterenol exposure, phospholamban contained approximately equimolar amounts of these two phosphoamino acids. Two major tryptic phosphopeptides containing greater than 90% of the incorporated radioactivity were obtained from phospholamban labeled in intact ventricles. The amino acid sequences of these two tryptic peptides corresponded exactly to residues 14-25 and 15-25 of canine cardiac phospholamban, thus localizing the sites of in situ phosphorylation to serine 16 and threonine 17. Phosphorylation of phospholamban at two sites in heart perfused with isoproterenol was supported by detection of 11 distinct mobility forms of the pentameric protein by use of the Western blotting method, consistent with each phospholamban monomer containing two phosphorylation sites, and with each pentamer containing from 0 to 10 incorporated phosphates. Our results localize the sites of in situ phospholamban phosphorylation to serine 16 and threonine 17 and, furthermore, are consistent with the phosphorylations of these 2 residues being catalyzed by cAMP- and Ca2+/calmodulin-dependent protein kinases, respectively.

The Escherichia coli enterobactin biosynthesis gene, entD: nucleotide sequence and membrane localization of its protein product

The nucleotide sequence of the Escherichia coli enterobactin biosynthesis gene entD has been determined. entD specifies a predicted 23579 Dalton protein containing several helical regions, a transmembrane segment and one positively charged domain. The EntD polypeptide was overexpressed and identified in electrophoretic gels as a membrane protein. Although results of conventional membrane fractionation techniques were inconclusive, protease accessibility studies provided evidence that EntD domains are exposed on the inner leaflet of the cytoplasmic membrane. The presence of repetitive extragenic palindromic (REP) sequences within the fepA-entD intercistronic region was confirmed. Lack of a canonical promoter and an iron control region 5' to entD, along with RNA hybridization data, suggest that an iron-regulated transcript contains both fepA and entD.

Synthesis of phosphopeptides containing O-phosphoserine or O-phosphothreonine

Peptides containing phosphoserine or phosphothreonine were synthesized by solid phase methods. Phosphoserine and phosphothreonine were incorporated into peptides using Boc-diphenylphosphono esters of serine and threonine and standard DCC/HOBt coupling. The phenylphosphoesters were not removed when the peptides were cleaved from the resin by HF or by trifluoromethane sulfonic acid, but were subsequently removed by catalytic hydrogenation. Phosphopeptides were purified by HPLC and by Fe+3-Chelex chromatography and their identity verified by mass spectrometry. Two peptides, Leu-Arg-Arg-Ala-Ser(P)-Leu-Gly and Leu-Arg-Arg-Ala-Thr(P)-Leu-Gly, were prepared by both enzymatic and chemical methods and had identical properties.

L-serine analogues form Schiff base and quinonoidal intermediates with Escherichia coli tryptophan synthase

Substrate analogues of L-serine have been found that react with the alpha 2 beta 2 complex of Escherichia coli tryptophan synthase. Upon reaction with alpha 2 beta 2, the analogues glycine, L-histidine, L-alanine, and D-histidine form chemical intermediates derived from reaction with enzyme-bound pyridoxal 5'-phosphate with characteristic UV-visible spectral bands. The spectra of the products of the glycine, L-histidine, and L-alanine reactions with alpha 2 beta 2 contain contributions from the external aldimine, the quinonoid species, and other intermediates along the catalytic pathway. Just as previously reported for the reaction of L-serine with beta 2 [Goldberg, M. E., York, S., & Stryer, L. (1968) Biochemistry 7, 3662-3667], the reactions of glycine, L-histidine, and L-alanine with the beta 2 form of tryptophan synthase yield spectra with no contributions from catalytic intermediates beyond the external aldimine. The kinetics of intermediate formation and comparisons of the time courses for the exchange of alpha-1H for solvent 2H catalyzed by alpha 2 beta 2 or beta 2 were found to be consistent with these assignments. Intermediates further along the tryptophan synthase catalytic pathway are stabilized to a greater degree in the alpha 2 beta 2 complex than in the beta 2 species alone. This observation strongly suggests that the association of alpha and beta subunits to form the native alpha 2 beta 2 species lowers the activation energies for the interconversion of the external aldimine with chemical species further along the catalytic path.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleotide sequence of the Escherichia coli entE gene

The Escherichia coli entE gene encodes a polypeptide necessary in the latter stages of biosynthesis of the siderophore enterobactin. The entE gene and adjacent DNA were sequenced. The predicted EntE polypeptide consists of 536 amino acids and has a Mr of 58,299 and a net charge of -7.33. Genetic evidence combined with this and previous sequencing data indicate that the genes entCEB(G)A are transcribed as unit from a promoter upstream of entC.

Immune response to the iron-deprivation-induced proteins of Salmonella typhi in typhoid fever

Iron starvation conditions limited the growth of Salmonella typhi, as evidenced by an increase in the lag phase of a culture and a decrease in the number of bacteria reached in the stationary phase. The analysis of the outer membrane of bacteria grown under these conditions identified new protein components with apparent molecular weights of 83,000, 78,000, and 69,000. The extent of induction of these proteins was regulated by increased iron deprivation. Immunoblot analysis showed that the serum of patients with typhoid fever exhibited an immunoglobulin G response to these iron-deprivation-induced proteins. The results of bioassays and DNA-DNA hybridization experiments indicated that pathogenic strains of S. typhi produced enterochelin but not aerobactin. Immunodetection with an anti-FepA antiserum confirmed that one of the induced proteins is the S. typhi analog of the Escherichia coli fepA gene product. These studies suggest a role for iron uptake in the pathogenesis of typhoid fever and confirm the immunogenicity of some of the outer membrane proteins of this pathogen.

An intramolecular hydrogen bond with large proton polarizability within the head group of phosphatidylserine. An infrared investigation

Films of O-phospho-L-serine-P-ethylester (PSE) were studied by infrared spectroscopy. PSE films were studied pure and as 1:1 mixture with LiOH, NaOH, KOH, and Ca(OH)2 as a function of the degree of hydration. The same investigations were performed if (L-glu)n was added to the system (ratio 1:1, PSE/glu residue). In the PSE molecules an intramolecular (I) COOH...-OP in equilibrium with COO-...HOP (II) hydrogen bond is present. In this bond a double minimum proton potential occurs and it shows large proton polarizability. This hydrogen bond is relatively stable as shown by the neutralization experiments. At low degree of hydration the cations are present at the phosphate groups. The Li ions polarize the intramolecular hydrogen bonds much more than the other cations, i.e., the weight of the proton-limiting structure COOH...-OP is increased by Li ions. Regarding these results one has to assume that such a hydrogen bond is also present in the phosphatidylserine head groups. It is discussed that such hydrogen bonds could be part of a lateral charge-conducting system in the polar surfaces of biological membranes. Such systems could connect proton-creating and proton-consuming centers at the membrane surface and conduct positive charge at an extremely high rate.

A new antitumor antibiotic, FR900840. II. Structural elucidation of FR900840

The structure of FR900840, a new antitumor antibiotic produced by a strain of Streptomyces has been deduced as 1 on the basis of spectroscopic and chemical evidence and finally confirmed by synthesis from L-threonine and L-serine.

A new antitumor antibiotic, FR900840. III. Antitumor activity against experimental tumors

FR900840 [2S)-2-amino-2-carboxyethyl (3R)-2-diazo-3-hydroxybutyrate), a new antibiotic with antitumor activity was isolated from the fermentation broth of Streptomyces sp. No. 8727. Its antitumor activity was examined in three mouse tumor systems and ten human tumor systems. FR900840 had no clear effect on mouse ascitic tumors, P388 and L1210, and the B16 melanoma line, but had prominent antitumor effects on several human solid tumors. Its antitumor activity against A549 human lung adenocarcinoma was stronger than those of vinblastine, doxorubicin and cisplatin. These results suggest that FR900840 may become a useful prototype antitumor drug.

A new antitumor antibiotic, FR900840. I. Discovery, identification, isolation and characterization

A new antitumor antibiotic, FR900840, was isolated from a culture broth of Streptomyces strain No. 8727 as a pale yellowish prism and the molecular formula was determined to be C7H11N3O5. The antibiotic exhibited prominent antitumor effects on human tumor cell lines both in vitro and in vivo.

Tumor necrosis factor signal transduction. Tissue-specific serine phosphorylation of a 26-kDa cytosolic protein

Binding of tumor necrosis factor-alpha (TNF-alpha) to its receptor on U937 cells results in rapid and TNF dose-dependent phosphorylation of a cytosolic protein with an apparent molecular mass of 26,000 kDa (p26) and an isoelectric point of 5.6. Half-maximal phosphorylation of p26 was achieved at concentrations of 1.8 ng/ml and was detectable within 20 s of TNF-alpha treatment. p26 is phosphorylated exclusively at serine residues. p26 phosphorylation occurs at 37 degrees C as well as at 14 degrees C, indicating that internalization of the TNF receptor is not required for serine kinase activation. Dephosphorylation of p26 starts 10 min after TNF-induced phosphorylation, suggesting a possible regulatory function of this cytosolic protein within the post-TNF receptor signaling system. p26 is also phosphorylated upon treatment with lymphotoxin. In contrast, both interferon-gamma and lipopolysaccharide fail to induce p26 phosphorylation. Whereas phosphorylated p26 was detected in the TNF-sensitive breast cancer cell line CRL1500, other TNF-responsive tumor cell lines investigated lacked enhanced phosphorylation of p26 in response to TNF, indicating that the 26-kDa phosphoprotein (pp26) may be a cell type-specific second messenger molecule involved in TNF signal transduction in some, but not all, target cells. p26 is also phosphorylated in a subclone of U937 (U937.C27) that responds to TNF-alpha with differentiation, yet is resistant to TNF-alpha-mediated growth inhibition. In contrast, p26 is not phosphorylated in another U937 derivative (U937.G3) that is resistant to both TNF-alpha-induced growth arrest and differentiation, suggesting that pp26 may play a role in the TNF signaling pathway linked to differentiation processes rather than to growth control.

Serine and tyrosine phosphorylation of 28- and 35-kDa proteins of human T lymphocytes stimulated by streptococcal M protein

Purified polypeptide fragments of certain surface M proteins of group A streptococci stimulate blastogenesis and the differentiation of cytotoxic T lymphocytes of normal human lymphocytes. The biochemical basis of lymphocyte stimulation by a type M5 protein polypeptide fragment (pep M5) was investigated. Optimal blastogenic doses of pep M5 or phytohemagglutinin stimulated the phosphorylation of several cellular proteins. However, pep M5 but not phytohemagglutinin induced the phosphorylation of 28- and 35-kDa proteins. The 28-kDa protein was shown to be phosphorylated only at serine residues, whereas the 35-kDa protein was phosphorylated only at tyrosine residues. Stimulation of peripheral blood lymphocytes with pep M5 caused a two-fold increase in the CD8+ and CD4+ 4B4+ subpopulations of T lymphocytes. The phosphorylation of the 28-kDa protein appeared to be confined to the CD4+ T cell subpopulation.

Thin-layer chromatography can resolve phosphotyrosine, phosphoserine, and phosphothreonine in a protein hydrolyzate

A solution of propionic acid, 1 M ammonium hydroxide, and isopropyl alcohol (45/17.5/17.5, v/v) was the ascending solvent in the separation of phosphotyrosine, phosphothreonine, and phosphoserine by thin-layer chromatography. The immobile phase was cellulose. The relative migrations were 0.44, 0.38, and 0.2, respectively. A previously described thin-layer system consisting of isobutyric acid and 0.5 M ammonium hydroxide (50/30, v/v) gave very similar relative migrations. To determine the usefulness of thin-layer chromatography in phosphoamino acid analysis, the propionic acid/ammonium hydroxide/isopropyl alcohol solution was used to characterize phosphorylated residues in a plasma membrane protein which is a substrate for the insulin receptor kinase, in insulin receptor phosphorylated histone H2B, and in an in vivo phosphorylated 90000-Da protein from IM9 cells. 32P-labeled proteins were separated by dodecyl sulfate-gel electrophoresis, digested with trypsin, and then hydrolyzed with 6 N HCl, 2 h, 110 degrees C. Following thin-layer chromatography of the hydrolyzates and autoradiography, phosphotyrosine was detected in insulin receptor substrates, and phosphoserine and phosphothreonine were found in the in vivo-phosphorylated protein. This study supports previous reports about the practicality of thin-layer chromatography in phosphoamino acid analysis and it demonstrates that a propionic acid, ammonium hydroxide, isoprophyl alcohol solution may be a useful ascending solvent mixture for this purpose.

Correlation between histidine operon expression and guanosine 5'-diphosphate-3'-diphosphate levels during amino acid downshift in stringent and relaxed strains of Salmonella typhimurium

We have analyzed the correlation of attenuator-independent expression of the Salmonella typhimurium histidine operon in vivo with levels of the "alarmone" guanosine 5'-diphosphate 3'-diphosphate. Amino acid downshift caused by serine hydroxamate addition increased his expression in a relA+ strain and decreased his expression in a relA mutant, whereas levels of guanosine 5'-diphosphate-3'-diphosphate varied in parallel with the changes in his expression in the two strains. In several experiments, overall variations in his expression ranged from 20- to 60-fold after downshift. The mild downshift allowed growth of the cultures to continue at near-preshift rates. Serine hydroxamate addition was also used to analyze the effect of amino acid downshift on induced expression of wild-type and mutant lac promoters. There was a 12-fold difference in lac expression when a relA+-relA1 pair was subjected to mild starvation but only a 3-fold difference when the strains carried the lacZpL8UV5 promoter mutation. These results suggest that guanosine 5'-diphosphate-3'-diphosphate stimulates gene expression in vivo at the level of transcription initiation.

Nucleotide sequence and transcriptional organization of the Escherichia coli enterobactin biosynthesis cistrons entB and entA

The nucleotide sequence of a 2,137-base-pair DNA fragment expressing enterobactin biosynthesis functions defined the molecular boundaries and translational products of the entB and entA genes and identified a closely linked downstream open reading frame encoding an uncharacterized protein of approximately 15,000 daltons (P15). The sequence revealed that an independent protein-coding sequence corresponding to an EntG polypeptide was not situated in the genetic region between the entB and entA cistrons, to which the EntG- phonotype had been genetically localized. As a result, the biochemical nature of the EntG function in the biosynthetic pathway requires reevaluation. The EntA polypeptide displayed significant similarities at the amino acid level to the pyridine nucleotide-binding domains of several members of a family of alcohol-polyol-sugar dehydrogenase enzymes, consistent with its function as the enzyme catalyzing the final step of dihydroxybenzoate biosynthesis. An additional role for EntA in the isochorismate synthetase activity of EntC was strongly implicated by genetic evidence. Evidence from the nucleotide sequence of this region and newly constructed ent-lacZ fusion plasmids argues strongly that these genes are linked in an iron-regulated entCEBA (P15) polycistronic operon.

Nucleotide sequence of a cluster of Escherichia coli enterobactin biosynthesis genes: identification of entA and purification of its product 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase

The nucleotide sequence of a region of the Escherichia coli chromosome encoding part of a cluster of genes involved in the biosynthesis of the iron chelator enterobactin has been determined. Four closely linked open reading frames, corresponding to the coding regions of entE (carboxy-terminal 144 amino acids), entB (32,554 daltons), entA (26,249 daltons), and an unidentified gene (P15) encoding a 14,970-dalton protein, were found. The lack of intergenic sequences and promoterlike elements suggests that these genes form part of the same transcription unit. We report the purification to homogeneity of the entA product, 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase. It is an octamer of native molecular weight 210,000; the amino-terminal amino acid sequence confirmed the entA coding region. No isochorismate synthase activity was associated with this polypeptide. This finding leads to the conclusion that the recent suggestion (M. S. Nahlik, T. P. Fleming, and M. A. McIntosh, J. Bacteriol. 169:4163-4170, 1987) that 2,3-dihydro-2,3-dihydroxybenzoate dehydrogenase and isochorismate synthase activities reside on a single 26,000-dalton bifunctional enzyme is incorrect, even though the entA and entC mutations map to the same genetic locus.

Phosphorylation at serine 89 induces a shift in gel mobility but has little effect on the function of adenovirus type 5 E1A proteins

Phosphorylation at serine 89 was shown to be the major cause of the shift in gel migration of the 289R and 243R early region 1A (E1A) proteins of human adenovirus type 5. However, conversion of Ser-89 to alanine by site-directed mutagenesis did not abolish E1A transactivating or transforming activities, suggesting that phosphorylation at this site is not necessary for these E1A functions.

Characterization of sites of serine phosphorylation in human placental insulin receptor copurified with insulin-stimulated serine kinase activity by two-dimensional thin-layer peptide mapping

Insulin receptor was copurified from human placenta together with insulin-stimulated kinase activity that phosphorylates the insulin receptor on serine residues. Analysis of phosphorylated insulin receptor by two-dimensional tryptic peptide mapping showed that sites of insulin stimulated serine phosphorylation in the insulin receptor were recovered in the same peptides as those known to be phosphorylated on serine in vivo in response to insulin. This indicates that the serine kinase copurified with the insulin receptor represents a physiologically important enzyme involved in the insulin triggered serine phosphorylation of the insulin receptor in vivo.

Identification of N-(2-propenal)ethanolamine as a urinary metabolite of malondialdehyde

N-(2-propenal)ethanolamine was isolated from rat and human urine using anion exchange, cation exchange, size exclusion and high performance liquid chromatography. Acid hydrolysis of the isolate yielded malondialdehyde (MDA) and ethanolamine (E) in a 1:1 molar ratio. A 1:1 E-MDA adduct was synthesized and found to be chromatographically inseparable from the urinary metabolite. Its NMR and UV spectra and lack of fluorescence were consistent with those of an enaminal formed by a Schiff's base reaction. The identification in urine of an adduct of MDA with ethanolamine, and the previous identification of an adduct with serine, constitutes direct evidence for the oxidative decomposition in vivo of polyunsaturated fatty acids present in the relevant phospholipids. The absence in urine of MDA adducts with other alpha-amino compounds (at least in comparable amounts) indicates that the ethanolamine and serine derivatives are formed in situ and not as a result of reactions with MDA generated in enzymatic processes.

Phosphoserine as a recognition determinant for glycogen synthase kinase-3: phosphorylation of a synthetic peptide based on the G-component of protein phosphatase-1

Prior phosphorylation of its substrate has been shown to be important for substrate recognition by the protein kinase glycogen synthase kinase-3 (GSK-3). Phosphorylation of glycogen synthase by GSK-3 is known to be enhanced by the previous action of casein kinase II and the sequence -SXXXS(P)- was proposed as the minimal recognition determinant for GSK-3. The glycogen binding subunit of type 1 phosphoprotein phosphatase has been shown to be phosphorylated by cyclic AMP-dependent protein kinase at serine-13 in the sequence KPGFS(5)PQPS(9)RRGS(13)ESSEEVYV (F.B. Caudwell, A. Hiraga, and P. Cohen (1986) FEBS Lett. 194, 85-89). Inspection of the sequence revealed potential GSK-3 sites at residues 5 and 9. Using a synthetic peptide with the above sequence, we found that phosphorylation of serine-13 by cyclic AMP-dependent protein kinase permitted the recognition of serine-9 and serine-5 by GSK-3. The work provides another example of a substrate for GSK-3 and demonstrates that the action of GSK-3 is linked to the presence of phosphate in the substrate and not the action of any particular protein kinase. In the course of the analyses, a novel feature of trypsin cleavage of phosphopeptides was noted. In the sequence -SRRGS(P)- trypsin acted uniquely after the first arginine whereas in the sequence -S(P)RRGS(P)- it cleaved randomly at either arginine residue. The fact that GSK-3 could phosphorylate a peptide derived from a phosphatase subunit also raises the possibility that GSK-3 might be involved in controlling glycogen-associated type 1 phosphatase and, more generally, in mediating cyclic AMP control of protein phosphorylation in cells.

Phosphorylatable serine residues are located in a non-helical tailpiece of a catch muscle myosin

Myosin from a molluscan catch muscle displays unusual properties: when phosphorylated in the rod by an endogenous heavy-chain kinase, myosin solubility is enhanced and the molecule folds (Castellani & Cohen, Proc. natn. Acad. Sci. U.S.A. 84, (1987) 4058-62). We have now localized the sites of phosphorylation to the carboxy-terminal end of the rod by selective proteolytic cleavage. Two major stretches of sequence, 18 and 21 residues long, have been identified, each containing a single residue of phosphoserine. Analysis of the amino-acid sequence of these two peptides indicates that they form a non-helical tailpiece. We discuss how phosphorylation of this tailpiece might influence enzymatic activity in catch muscle thick filaments.

Inhibitory effects of L-threo-DOPS, an L-noradrenaline precursor, on locus coeruleus-originating neurons in the caudate nucleus

Electrophysiological studies using reserpine-treated cats were carried out to elucidate the effects of L-threo-3,4-dihydroxyphenylserine (L-threo-DOPS) on the noradrenergic pathway from the locus coeruleus (LC) to the caudate nucleus (CN) neurons, which were activated by iontophoretically applied bromocriptine, a dopamine D-2 receptor agonist. In the CN neurons, glutamate-induced firing was inhibited by iontophoretic application of noradrenaline, but not by repetitive stimulation of the LC or iontophoretically applied L-threo-DOPS. After intraventricular administration of L-threo-DOPS, however, LC stimulation inhibited the glutamate-induced firing. These results suggest that L-noradrenaline that was produced from the conversion of L-threo-DOPS inhibited the CN neurons which possess dopamine D-2 receptors.

d,l-threo-3,4-dihydroxyphenylserine restores sympathetic control and cures orthostatic hypotension in dopamine beta-hydroxylase deficiency

Two patients with congenital dopamine beta-hydroxylase (DBH) deficiency were treated with d,l-threo-3,4-dihydroxyphenylserine (DOPS), 500 mg twice daily. In this orthostatic syndrome the functional integrity of the sympathetic noradrenergic neuron is probably intact, but dopamine instead of noradrenaline is released as the neurotransmitter. In vitro l-DOPS may serve as a substrate for aromatic-l-amino-acid decarboxylase (ALAAD) to form physiological (-)-noradrenaline. During infusion of d,l-threo-DOPS, 400 mg in 4 h, noradrenaline appeared in plasma and blood pressure rose, whereas plasma dopamine and the elevated venous:arterial ratio of plasma dopamine decreased. During chronic treatment supine blood pressure rose from 100-115/55-65 to 140-145/80-85 mmHg and orthostatic hypotension disappeared. After 12 and 6 months of treatment the patients are free of symptoms and they live a normal life. During chronic treatment, d,l-threo-DOPS, like plasma noradrenaline and dopamine, rose after standing, indicating release of the precursor after neuronal stimulation. After administration of tyramine plasma noradrenaline, dopamine and d,l-threo-DOPS and their respective venous:arterial ratios rose; this is further evidence of neuronal release. Thus, in DBH deficiency, dopamine instead of noradrenaline is released as a neurotransmitter, but the integrity of the sympathetic neuron is otherwise intact. Acting as an alternative substrate for ALAAD in the production of noradrenaline, DOPS is taken up by the neuron, restoring sympathetic control and thereby curing the orthostatic hypotension in DBH deficiency.