Putting the brakes on reproduction: Implications for conservation, global climate change and biomedicine

Seasonal breeding is widespread in vertebrates and involves sequential development of the gonads, onset of breeding activities (e.g. cycling in females) and then termination resulting in regression of the reproductive system. Whereas males generally show complete spermatogenesis prior to and after onset of breeding, females of many vertebrate species show only partial ovarian development and may delay onset of cycling (e.g. estrous), yolk deposition or germinal vesicle breakdown until conditions conducive for ovulation and onset of breeding are favorable. Regulation of this "brake" on the onset of breeding remains relatively unknown, but could have profound implications for conservation efforts and for "mismatches" of breeding in relation to global climate change. Using avian models it is proposed that a brain peptide, gonadotropin-inhibitory hormone (GnIH), may be the brake to prevent onset of breeding in females. Evidence to date suggests that although GnIH may be involved in the regulation of gonadal development and regression, it plays more regulatory roles in the process of final ovarian development leading to ovulation, transitions from sexual to parental behavior and suppression of reproductive function by environmental stress. Accumulating experimental evidence strongly suggests that GnIH inhibits actions of gonadotropin-releasing hormones on behavior (central effects), gonadotropin secretion (central and hypophysiotropic effects), and has direct actions in the gonad to inhibit steroidogenesis. Thus, actual onset of breeding activities leading to ovulation may involve environmental cues releasing an inhibition (brake) on the hypothalamo-pituitary-gonad axis.

An evolutionary scenario for gonadotrophin-inhibitory hormone in chordates

In 2000, we discovered a novel hypothalamic neuropeptide that actively inhibits gonadotrophin release in quail and termed it gonadotrophin-inhibitory hormone (GnIH). GnIH peptides have subsequently been identified in most representative species of gnathostomes. They all share a C-terminal LPXRFamide (X = L or Q) motif. GnIH can inhibit gonadotrophin synthesis and release by decreasing the activity of GnRH neuroes, as well as by directly inhibiting pituitary gonadotrophin secretion in birds and mammals. To investigate the evolutionary origin of GnIH and its ancestral function, we identified a GnIH precursor gene encoding GnIHs from the brain of sea lamprey, the most ancient lineage of vertebrates. Lamprey GnIHs possess a C-terminal PQRFamide motif. In vivo administration of one of lamprey GnIHs stimulated the expression of lamprey GnRH in the hypothalamus and gonadotophin β mRNA in the pituitary. Thus, GnIH may have emerged in agnathans as a stimulatory neuropeptide that subsequently diverged to an inhibitory neuropeptide during the course of evolution from basal vertebrates to later-evolved vertebrates, such as birds and mammals. From a structural point of view, pain modulatory neuropeptides, such as neuropeptide FF (NPFF) and neuropeptide AF, share a C-terminal PQRFamide motif. Because agnathans possess both GnIH and NPFF genes, the origin of GnIH and NPFF genes may date back before the emergence of agnathans. More recently, we identified a novel gene encoding RFamide peptides in the amphioxus. Molecular phylogenetic analysis and synteny analysis indicated that this gene is closely related to the genes of GnIH and NPFF of vertebrates. The results suggest that the identified protochordate gene is similar to the common ancestor of GnIH and NPFF genes, indicating that the origin of GnIH and NPFF may date back to the time of the emergence of early chordates. The GnIH and NPFF genes may have diverged by whole-genome duplication during the course of vertebrate evolution.

Identification, localisation and functional implication of 26RFa orthologue peptide in the brain of zebra finch (Taeniopygia guttata)

Several neuropeptides with the C-terminal Arg-Phe-NH(2) (RFa) sequence have been identified in the hypothalamus of a variety of vertebrates. The present study was conducted to isolate novel RFa peptides from the zebra finch brain. Peptides were isolated by immunoaffinity purification using an antibody that recognises avian RFa peptides. The isolated peptide consisted of 25 amino acids with RFa at its C-terminus. The sequence was SGTLGNLAEEINGYNRRKGGFTFRFa. Alignment of the peptide with vertebrate 26RFa has revealed that the identified peptide is the zebra finch 26RFa. We also cloned the precursor cDNA encoding this peptide. Synteny analysis of the gene showed a high conservation of this gene among vertebrates. In addition, we cloned the cDNA encoding a putative 26RFa receptor, G protein-coupled receptor 103 (GPR103) in the zebra finch brain. GPR103 cDNA encoded a 432 amino acid protein that has seven transmembrane domains. In situ hybridisation analysis in the brain showed that the expression of 26RFa mRNA is confined to the anterior-medial hypothalamic area, ventromedial nucleus of the hypothalamus and the lateral hypothalamic area, the brain regions that are involved in the regulation of feeding behaviour, whereas GPR103 mRNA is distributed throughout the brain in addition to the hypothalamic nuclei. When administered centrally in free-feeding male zebra finches, 26RFa increased food intake 24 h after injection without body mass change. Diencephalic GPR103 mRNA expression was up-regulated by fasting for 10 h. Our data suggest that the hypothalamic 26RFa-its receptor system plays an important role in the central control of food intake and energy homeostasis in the zebra finch.

Gonadotrophin-inhibitory hormone: a multifunctional neuropeptide

Gonadotrophin-inhibitory hormone (GnIH) was discovered 8 years ago in birds. Its identification raised the possibility that gonadotrophin-releasing hormone (GnRH) is not the sole hypothalamic neuropeptide that directly influences pituitary gonadotrophin release. Initial studies on GnIH focused on the avian anterior pituitary as comprising the only physiological target of GnIH. There are now several lines of evidence indicating that GnIH directly inhibits pituitary gonadotrophin synthesis and release in birds and mammals. Histological studies on projections from hypothalamic GnIH neurones subsequently implied direct actions of GnIH within the brain and in the periphery. In addition to actions on the pars distalis via the median eminence, GnIH axons and terminals are present in multiple brain areas in birds, and the GnIH receptor is expressed on GnRH-I and -II neurones. Furthermore, we have demonstrated the presence of GnIH and its receptor in avian and mammalian gonads. Thus, GnIH can act directly at multiple levels: within the brain, on the pituitary and in the gonads. In sum, our data indicate that GnIH and its related peptides are important modulators of reproductive function at the level of the GnRH neurone, the gonadotroph and the gonads. Here, we provide an overview of the known levels of GnIH action in birds and mammals. In addition, environmental and physiological factors that are involved in GnIH regulation are reviewed.

A new key neurohormone controlling reproduction, gonadotrophin-inhibitory hormone in birds: discovery, progress and prospects

In vertebrates, the neuropeptide control of gonadotrophin secretion is primarily through the stimulatory action of the hypothalamic decapeptide, gonadotrophin-releasing hormone (GnRH). Gonadal sex steroids and inhibin inhibit gonadotrophin secretion via feedback from the gonads, but a hypothalamic neuropeptide inhibiting gonadotrophin secretion was, until recently, unknown in vertebrates. In 2000, we discovered a novel hypothalamic dodecapeptide that directly inhibits gonadotrophin release in quail and termed it gonadotrophin-inhibitory hormone (GnIH). GnIH acts on the pituitary and GnRH neurones in the hypothalamus via a novel G-protein-coupled receptor for GnIH to inhibit gonadal development and maintenance by decreasing gonadotrophin release and synthesis. The pineal hormone melatonin is a key factor controlling GnIH neural function. GnIH occurs in the hypothalamus of several avian species and is considered to be a new key neurohormone inhibiting avian reproduction. Thus, the discovery of GnIH provides novel directions to investigate neuropeptide regulation of reproduction. This review summarises the discovery, progress and prospects of GnIH, a new key neurohormone controlling reproduction.

Production of hypotaurine, taurine and sulfate in rats and mice injected with L-cysteinesulfinate

We studied in vivo production of taurine, hypotaurine and sulfate following subcutaneous administration of L-cysteinesulfinate (CSA) to rats and mice. When 5.0 mmol/kg of body weight of CSA was injected to rats, increased urinary excretions of taurine, hypotaurine and sulfate in 24 h urine were 617, 52 and 1,767 micromol/kg, respectively. From these results together with our previous data, sulfate production was calculated to be 1.6 times greater than taurine production. Increased contents (micromol/g of wet tissue) over the control of taurine and hypotaurine in mouse tissues at 60 min after the injection of 5.0 mmol/kg body weight of CSA were: liver, 3.5 and 9.9; kidney, 0.3 and 5.2; heart, 3.7 and 0.2; blood plasma, 0.4 and 0.2, respectively. Upon loading of hypotaurine or taurine, tissue contents of these amino acids in liver and kidney increased greatly. Our results indicate that liver is the most active tissue for taurine production, followed by kidney, and that external CSA, hypotaurine and taurine are easily taken up by these tissues.

A novel G protein-coupled receptor for gonadotropin-inhibitory hormone in the Japanese quail (Coturnix japonica): identification, expression and binding activity

We recently identified a novel hypothalamic dodecapeptide inhibiting gonadotropin release in the Japanese quail (Coturnix japonica). This novel peptide was therefore named gonadotropin-inhibitory hormone (GnIH). The GnIH precursor encoded one GnIH and two GnIH-related peptides (GnIH-RP-1 and GnIH-RP-2) that shared the same C-terminal motif, Leu-Pro-Xaa-Arg-Phe-NH(2) (Xaa=Leu or Gln; LPXRF-amide peptides). Identification of the receptor for GnIH is crucial to elucidate the mode of action of GnIH. We therefore identified the receptor for GnIH in the quail diencephalon and characterized its expression and binding activity. We first cloned a cDNA encoding a putative GnIH receptor by a combination of 3' and 5' rapid amplification of cDNA ends (RACE) using PCR primers designed from the sequence for the receptor for rat RF-amide-related peptide (RFRP), an orthologous peptide of GnIH. Hydrophobic analysis revealed that the putative GnIH receptor possessed seven transmembrane domains, indicating a new member of the G protein-coupled receptor superfamily. The crude membrane fraction of COS-7 cells transfected with the putative GnIH receptor cDNA specifically bound to GnIH and GnIH-RPs in a concentration-dependent manner. Scatchard plot analysis of the binding showed that the identified GnIH receptor possessed a single class of high-affinity binding sites (K(d)=0.752 nM, B(max)=24.8 fmol/mg protein). Southern blotting analysis of reverse transcriptase-mediated PCR products revealed the expression of GnIH receptor mRNA in the pituitary gland and several brain regions including diencephalon in the quail. These results suggest that GnIH acts directly on the pituitary via GnIH receptor to inhibit gonadotropin release. GnIH may also act on the hypothalamus to inhibit gonadotropin-releasing hormone release.

Gonadotrophin inhibitory hormone depresses gonadotrophin alpha and follicle-stimulating hormone beta subunit expression in the pituitary of the domestic chicken

Studies performed in vitro suggest that a novel 12 amino acid RF amide peptide, isolated from the quail hypothalamus, is a gonadotrophin inhibitory hormone (GnIH). The aim of the present study was to investigate this hypothesis in the domestic chicken. Injections of GnIH into nest-deprived incubating hens failed to depress the concentration of plasma luteinizing hormone (LH). Addition of GnIH to short-term (120 min) cultures of diced pituitary glands from adult cockerels depressed follicle-stimulating hormone (FSH) and LH release and depressed common alpha and FSHbeta gonadotrophin subunit mRNAs, with no effect on LHbeta subunit mRNA. Hypothalamic GnIH mRNA was higher in incubating (out-of-lay) than in laying hens, but there was no significant difference in the amount of hypothalamic GnIH mRNA in out-of-lay and laying broiler breeder hens at the end of a laying year. It is concluded that avian GnIH may play a role in controlling gonadotrophin synthesis and associated constitutive release in the domestic chicken.

Developmental changes in gonadotropin-inhibitory hormone in the Japanese quail (Coturnix japonica) hypothalamo-hypophysial system

We previously isolated a novel dodecapeptide containing a C-terminal -Arg-Phe-NH(2) sequence, SIKPSAYLPLRF-NH(2) (RFamide peptide), from the Japanese quail (Coturnix japonica) brain. This novel quail peptide was shown to be located in neurons of the paraventricular nucleus (PVN) and their terminals in the median eminence (ME), and to decrease gonadotropin release from cultured anterior pituitary in adult birds. We therefore designated this peptide gonadotropin-inhibitory hormone (GnIH). Furthermore, a cDNA encoding the GnIH precursor polypeptide has been characterized. To understand the physiological roles of this peptide, in the present study we analyzed developmental changes in the expressions of GnIH precursor mRNA and the mature peptide GnIH during embryonic and posthatch ages in the quail diencephalon including the PVN and ME. GnIH precursor mRNA was expressed in the diencephalon on embryonic day 10 (E10) and showed a significant increase on E17, just before hatch. GnIH was also detected in the diencephalon on E10 and increased significantly around hatch. Subsequently, the diencephalic GnIH content decreased temporarily, and again increased progressively until adulthood. GnIH-like immunoreactive (GnIH-ir) neurons were localized in the PVN on E10, but GnIH-ir fibers did not extend to the ME. However, GnIH-ir neurons increased in the PVN on E17, just before hatch, and GnIH-ir fibers extended to the external layer of the ME, as in adulthood. These results suggest that GnIH begins its function around hatch and acts as a hypothalamic factor to regulate gonadotropin release in the bird.

A study on the estimation of sulfur-containing amino acid metabolism by the determination of urinary sulfate and taurine

Sulfate and taurine are major end products of sulfur-containing amino acid metabolism in mammals including humans, and they are excreted in urine. Average excretions micromol/mg of creatinine) in the morning urine of 58 female college students were: total (free plus ester) sulfate (a). 12.53 +/- 3.85; free sulfate, 11.57 +/- 3.69; taurine, 0.78 +/- 0.53. Ratio of total sulfate and taurine was 10 : 0.6. Regression lines obtained by plotting total sulfate, free sulfate, or total sulfate plus taurine against urea have shown that the former excretions are significantly correlated with urea excretion. Excretion of total sulfate at zero point of urea excretion (b). was 5.30, which corresponded to 42.3% of average excretion (12.53) and was assumed to be derived from dietary sulfate. The difference 7.23 (a - b) seemed to be derived from sulfur-containing amino acids. It was pointed out that the difference of average sulfate excretion and sulfate excretion at zero urea excretion, namely a - b, was appropriate for the metabolic index of sulfur-containing amino acids of the group examined. As free sulfate constituted 92.3% of total sulfate, excretion of ester sulfate was at a constant level, and that of taurine was not significantly correlated with urea excretion, the value of free sulfate corresponding to the value a - b of total sulfate mentioned above seemed to be a reliable and convenient index in the assessment of sulfur-containing amino acid metabolism.

Developmental changes in galanin in lumbosacral sympathetic ganglionic neurons innervating the avian uterine oviduct and galanin induction by sex steroids

We recently found lumbosacral sympathetic ganglionic galanin neurons innervating the quail uterine oviduct. Galaninergic innervation of the uterine muscle may be essential for avian oviposition, as galanin evoked oviposition through a mechanism of induction of vigorous uterine contraction. The questions arising from these findings are: what changes occur in galanin expression in the sympathetic ganglionic galanin neuron during development, and what is the hormonal factor(s) that induces galanin expression in this neuron? Therefore, the present study examined the developmental changes in galanin of the quail sympathetic ganglionic neuron and uterus, and the effect of administration of ovarian sex steroids on galanin induction. Immature birds reared under long-day photoperiods from 4 weeks of age demonstrated progressive increases in galanin levels both per unit ganglionic protein (concentration) and per ganglia (content) concurrent with ganglionic development during weeks 4--13. The uterine galanin content and uterine weight also increased progressively during the same period, but the galanin concentration in the uterus at 4 weeks was high due to the much smaller tissue mass. Immunocytochemical analysis with anti-galanin serum showed that immunoreactive ganglionic cells were few and small at 4 weeks and increased progressively thereafter. Administration of oestradiol-17 beta to immature birds at 3 weeks of age for 1 week increased both the galanin concentration and content in the ganglia without ganglionic growth. A marked increase in galanin-immunoreactive ganglionic cells was detected following oestradiol treatment. In contrast, progesterone increased ganglionic galanin levels, but the effects were low. Expression of the mRNAs encoding oestrogen receptor-alpha and -beta (ER alpha and ER beta) in the ganglionic tissue was verified by RT-PCR/Southern blot analysis. Immunocytochemical staining with anti-ER serum further revealed an intense immunoreaction restricted to the nucleus of ganglionic neurons. These results suggest that ovarian sex steroids, in particular oestradiol-17 beta, contribute as hormonal factors to galanin induction, which takes place in the lumbosacral sympathetic ganglionic neurons innervating avian uterine oviduct during development. Oestradiol may act directly on this ganglionic neuron through intra-nuclear receptor-mediated mechanisms to induce galanin.

Determination of hydrogen sulfide and acid-labile sulfur in animal tissues by gas chromatography and ion chromatography

A sensitive and reliable method was developed for the determination of hydrogen sulfide and acid-labile sulfur (ALS) in animal tissues using gas chromatography with flame photometric detector (GC-FPD) and ion chromatography (IC). Hydrogen sulfide trapped in alkaline solution was determined by GC-FPD as hydrogen sulfide or by IC as sulfate after oxidation with hydrogen peroxide. Sodium sulfide used as a source of hydrogen sulfide was standardized by IC. Fresh rat liver and heart tissues contained 112.2+/-23.0 and 274.1+/-34.6 nmol/g of ALS respectively. Free hydrogen sulfide was not detected.

Existence of galanin in lumbosacral sympathetic ganglionic neurons that project to the quail uterine oviduct

Oviposition in birds is conducted by vigorous contractions of the uterine oviduct. We recently isolated an oviposition-inducing peptide that was identified as avian galanin from mature quail oviducts. This peptide was localized in neuronal fibers terminating in muscle layers in the uterine oviduct and evoked vigorous uterine contractions through binding to receptors located in the uterus. However, no cell bodies that express avian galanin were detected in the uterus or other oviduct regions. To understand the control mechanism of avian oviposition by galanin, we identified the neurons that synthesize galanin and project to the uterus with the combination of retrograde labeling with neurobiotin and immunocytochemistry for galanin in mature Japanese quails. Retrograde labeling with neurobiotin from the uterus revealed that lumbosacral sympathetic ganglionic neurons located in the uterine side projected their axons to the uterine muscle layer. Abundant elementary granules were observed in somata of the retrogradely labeled sympathetic ganglionic neurons, suggesting that labeled neurons may function as a neurosecretory cell. Immunocytochemical analysis with the antiserum against avian galanin showed an intense immunoreaction restricted to somata of the retrograde-labeled ganglionic neurons. Preabsorbing the antiserum with avian galanin resulted in a complete absence of the immunoreaction. Competitive enzyme-linked immunosorbent assay using antigalanin serum confirmed that avian galanin existed in the sympathetic ganglionic neurons. Expression of the avian galanin messenger RNA in the neurons was further verified by Northern blot analysis. In addition, both avian galanin and its messenger RNA in the neurons were highly expressed in mature birds, unlike in immature birds. These results suggest that lumbosacral sympathetic ganglionic neurons innervating the uterine muscle produce avian galanin in mature birds. Because this peptide acts directly on the uterus to evoke oviposition through a mechanism of the induction of vigorous uterine contraction, galaninergic innervation of the uterine oviduct may be essential for avian oviposition.

Effects of thyroxine on L-cysteine desulfuration in mouse liver

The effect of exogenous thyroxine (T4) administration on the activity of rhodanese, cystathionase, and 3-mercaptopyruvate sulfurtransferase (MPST) in the mitochondrial and cytosolic fractions of mouse liver was investigated. Three groups of mice were treated for 6 consecutive days with subcutaneous injections of T4 (50 micrograms, 100 micrograms, and 250 micrograms per 100 g of body wt, respectively). The other 3 groups were given 100 micrograms of T4 per 100 g of body wt for 1, 2, or 3 days. The dose of 100 micrograms T4 per 100 g of body wt given for 6 days exerted the strongest effect on the activity of all of the investigated enzymes. In comparison to the control, rhodanese activity diminished in the mitochondrial fraction by 40% (P < 0.05), cystathionase activity diminished in the cytosolic fraction by 15% (P < 0.05), and MPST activity in the mitochondrial fraction was reduced by 34% (P < 0.05), whereas cytosolic MPST activity was unaltered. Simultaneously, in the liver homogenate, elevated levels of ATP and sulfate were observed after 6 days of T4 administration. Thus, the present results seem to suggest that in the mouse liver, after 6 days of administration of 100 micrograms T4 per 100 g of body wt, the desulfuration metabolism of L-cysteine is diminished, which is probably accompanied by an increase in oxidative L-cysteine metabolism. The dose of 100 micrograms per 100 g of body wt administered for a shorter period, and the use of a lower dosage (50 micrograms T4 per 100 g of body wt) for 6 days had a stimulatory effect upon MPST activity level, and an increased level of sulfane sulfur was observed.

Experimental beta-alaninuria induced by (aminooxy)acetate

Experimental beta-alaninuria was induced in rats by injection of (aminooxy)acetate (AOA), a potent inhibitor of aminotransferases, in order to elucidate the pathogenesis of hyper-beta-alaninemia. A 27-fold increase of beta-alanine (BALA) excretion was induced by subcutaneous injection of 1 5 mg of AOA per kg of body weight. A 13-fold and a 9-fold increase of beta-aminoisobutyric acid (BAIBA) and gamma-aminobutyric acid (GABA), respectively, were also induced simultaneously by the AOA injection. Identification of BALA and BAIBA isolated from the rat urine was performed by chromatographic and mass spectrometric analyses. The effects of AOA injection on the tissue levels of these amino acids were also studied. Contents of BALA in the liver and kidney and GABA in the brain increased significantly in response to AOA injection. The present study indicates that BALA transaminase is involved in hyper-beta-alaninemia.

Formation of gamma-glutamylpropargylglycylglycine from propargylglycine in human blood and erythrocytes

Gamma-Glutamylpropargylglycylglycine (gamma-Glu-PPG-Gly) was isolated as a metabolite of propargylglycine (2-amino-4-pentynoic acid, a natural and synthetic inhibitor of cystathionine gamma-lyase) from human blood incubated with D,L-propargylglycine in the presence of L-glutamate and glycine, and identified by fast-atom-bombardment mass spectrometry, indicating that human blood can metabolize propargylglycine to gamma-Glu-PPG-Gly. When whole blood was incubated with 2 mM D,L-propargylglycine in the presence of 10 mM L-glutamate and 10 mM glycine at 37 degrees C for 16h, 0.094+/-0.013 micromol of gamma-Glu-PPG-Gly was formed per ml of whole blood. When erythrocytes were incubated under the same conditions for 16h, 0.323+/-0.060 micromol of gamma-Glu-PPG-Gly was formed per ml of erythrocytes, suggesting a large contribution of erythrocytes to gamma-Glu-PPG-Gly formation in whole blood. The apparent Km value of gamma-Glu-PPG-Gly formation in human erythrocytes for D,L-propargylglycine was 0.32 mM. The observed rate of gamma-Glu-PPG-Gly formation and the Km value for D,L-propargylglycine suggest that metabolism of propargylglycine to gamma-Glu-PPG-Gly can play a definite biological role in human subjects who are loaded with propargylglycine.

Determination of glutathione peroxidase activity and its contribution to hydrogen peroxide removal in erythrocytes

A new method for the determination of glutathione peroxidase activity in erythrocytes was developed. The present method was applied to the measurement of hydrogen peroxide removal rates by glutathione peroxidase in erythrocytes at 70 microM hydrogen peroxide under simulated in vivo conditions. The removal rates by glutathione peroxidase in mouse erythrocytes were twenty-times faster than those in human ones and were 5.2 mumol/sec/g of Hb. The removal rates in acatalasemic mouse erythrocytes indicate that glutathione peroxidase is the main means of hydrogen peroxide removal in acatalasemic mouse erythrocytes. Based on these results, we concluded that glutathione peroxidase in mouse erythrocytes had sufficient ability to remove hydrogen peroxide at even relatively high concentrations. This may be one of the reasons why acatalasemic mice suffer no health problems while Japanese acatalasemic patients suffer from Takahara disease when infected with hydrogen peroxide-generating bacteria.

High-performance liquid chromatographic determination of beta-alanine, beta-aminoisobutyric acid and gamma-aminobutyric acid in tissue extracts and urine of normal and (aminooxy)acetate-treated rats

A method is described for the simultaneous determination of beta-alanine, beta-aminoisobutyric acid and gamma-aminobutyric acid in biological materials. Amino acids including these beta- and gamma-amino acids were derivatized with 4-dimethylaminoazobenzene-4'-sulfonyl (dabsyl) chloride and dabsyl amino acids formed were separated by reversed-phase high-performance liquid chromatography. Dabsyl derivatives of these beta- and gamma-amino acids were well separated from other dabsyl-amino acids. The method was applied to the determination of these beta- and gamma-amino acids in trichloroacetic acid extracts of various tissues and to the urine of normal rats and those injected with (aminooxy)acetate (AOA). AOA injection (15 mg per kg of body mass) produced remarkable increase in beta-alanine contents in liver, kidney and urine (10.2, 4.6 and 25.7 times, respectively).

Different effect of diastereoisomers of L-cystathionine sulfoxide on the stimulus coupled responses of human neutrophils

The priming effect of L-cystathionine sulfoxide, which is one of the unusual cystathionine metabolites found in the urine of patients with cystathioninuria, on the stimulus-induced superoxide generation by human neutrophils was examined. The synthetic L-cystathionine sulfoxide significantly enhanced the superoxide generations induced by N-formyl-methionyl-leucyl-phenylalanine [fMLP], opsonized zymosan [OZ], arachidonic acid [AA], and phorbol 12-myristate 13-acetate [PMA]. Then the synthetic L-cystathionine sulfoxide was separated into two diastereoisomers, CS-I and CS-II, which showed a peak at 76 and 83 min on chromatogram by amino acid analyzer, respectively. CS-I enhanced the superoxide generations induced by AA and PMA but not those induced by fMLP and OZ. On the contrary, CS-II enhanced the superoxide generations induced by fMLP and OZ but not those induced by AA and PMA. The superoxide generation induced by PMA with CS-I was suppressed by H-7 and was enhanced by genistein, while that by fMLP with CS-II was suppressed by genistein and was enhanced by H-7.

Determination of chiral catabolites from S-[2-carboxyl-1-(1H-imidazol-4-yl)ethyl]glutathione, a proposed metabolite of L-histidine, by capillary electrophoresis]

A new method for simultaneous determination of two diastereomers in each of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-L-cysteine (I) and N-¿S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-L-cysteinyl¿glycine (II) was developed by electrophoresis using a neutral coated capillary with a separation buffer, pH 6.00, containing 80 mM hydroxypropyl-beta-cyclodextrin at a field strength of 500 V cm-1 at 20 degrees C. This method was applied to establishment of a catabolic pathway from S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]glutathione (III) to compound I. Incubation of either of compound II diastereomers as an enzyme substrate with rat kidney homogenate in a phosphate buffer, pH 7.4, resulted in a formation of compound I only having correspondent configurations on asymmetric carbon atoms of its molecule with those of the substrate, i.e., no occurrence of isomerization in the catabolism. Additionally, little difference in action as the substrate between two diastereomers of compound II was found. When an equimolar mixture of two diastereomers of compound III was allowed to react with the homogenate in the presence of glycylglycine, two diastereomers of compound II were formed in the same yield with each other and then these were catabolized gradually to both isomers of compound I. These results suggest that compound II is a metabolic intermediate for the formation of compound I from compound III, and that little variation in reactivities of two diastereomers of compound III as well as compound II with enzymes is given by the difference in stereoisomerism of asymmetric carbon atoms on their molecules.

Excretion of sulfate and taurine in rats fed with a high protein diet

Sulfate and taurine are the main metabolites of L-cysteine in mammals and are excreted in the urine. The effect of a high protein diet on the ratio of sulfate to taurine excretion was studied in rats using synthetic 25% (standard protein diet group, group A) and 40% (high protein diet group, group B) casein diets. Average taurine and sulfate excretions (mumol/kg of body weight per day) were 280.4 +/- 93.8 and 943.2 +/- 144.8 in group A and 553.4 +/- 124.5 and 2675.0 +/- 390.9 in group B, respectively. Thus, the average taurine/sulfate ratio in group A was 0.30 +/- 0.08. By a single administration of 5 mmol of L-cysteine/kg of body weight in group A, the average taurine and sulfate excretions increased to 1127.5 +/- 120.2 and 4043.0 +/- 305.6, respectively, but the taurine/sulfate ratio changed only slightly (0.28). The average taurine/sulfate ratio in group B was 0.22 +/- 0.07, a significantly lower ratio than that in group A, which means that daily intake of a high protein diet resulted in more sulfate excretion. The taurine/sulfate ratio in group B was affected only slightly (0.19) by the cysteine administration as well. These results suggest that the ratio of taurine and sulfate production was determined by dietary protein content and that the increase in sulfate production is larger than that of taurine production when the intake of dietary protein is increased.

Excretion of taurine and sulfate in rats fed with a low protein diet

The effects of a low protein diet on the excretion of sulfate and taurine, major metabolites of L-cysteine in mammals, were studied in rats fed with synthetic 10% (group A) and 25% (group B) casein diets. The average excretions of total taurine (taurine plus hypotaurine) and total sulfate (free plus ester sulfate) (mumol/kg of body weight per day after the adaptation to the synthetic diet) in group A were 14.2 +/- 13.4 and 122.3 +/- 39.6, respectively, which were very low compared with 280.4 +/- 93.8 and 943.2 +/- 144.8, respectively, in group B. The taurine/sulfate ratio in group A was 0.12 +/- 0.11, which was significantly lower than that (0.30 +/- 0.08) in group B. A single intraperitoneal injection of 5 mmol of L-cysteine per kg of body weight in group A resulted in an increase in average taurine and sulfate excretion to 693.4 +/- 195.6 and 2440.6 +/- 270.0, respectively, and thus the average taurine/sulfate ratio increased to 0.29. These increases were transient and low taurine excretion resumed again 24 h after the L-cysteine administration. L-Cysteine injection in group B resulted in a similar increase in taurine and sulfate excretion, but the ratio changed only slightly (0.28). The present results suggest that in vivo production of taurine is reduced preferentially over sulfate production when sulfur amino acid supply is limited.

Effect of glucose-cysteine adduct on cysteine desulfuration in guinea pig tissues

Effect of intraperitoneal administration (12 mmol/kg of body weight) of glucose-cysteine adduct 2-(D-gluco-pentahydroxypentyl)-thiazolidine-4-carboxylate, (glc-cys) on the rhodanese, gamma-cystathionase and 3-mercaptopyruvate sulfurtransferase (MPST) activity levels in guinea pig tissues was studied. The rhodanese activity value in liver increased by 41%, 3-mercaptopyruvate sulfurtransferase by 24%, and gamma-cystathionase by 12% after three successive days of the administration. In the kidney, on the contrary, glc-cys administration resulted in about 18% decrease in the gamma-cystathionase activity value, whereas no changes in MPST and rhodanese activity values were observed. In the case of the brain, rhodanese and gamma-cystathionase did not change their activity but the activity of MPST decreased by 21%. MPST level did not change substantially in whole blood after glc-cys treatment. The results seem to indicate that in guinea pig liver but not in kidney and brain, glc-cys has a potential to activate the desulfuration pathway of L-cysteine metabolism.

Priming effect of N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine in human neutrophils and tyrosyl phosphorylation of 45 kDa protein

Human peripheral blood polymorphonuclear leukocytes were preincubated with N-acetylcystathionine and N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine (NAc-OCPC) found in the urine of a patient with cystathioninuria. NAc-OCPC significantly enhanced the N-formyl-methionyl-leucyl-phenylalanine-induced superoxide generation, whereas N-acetylcystathionine did not enhance the superoxide generation. When the cells were incubated with NAc-OCPC, the tyrosyl phosphorylation of 45 kDa protein of the cell was markedly increased with time. The phosphorylation process was dependent on the concentration of NAc-OCPC. Both the superoxide generation and the tyrosyl phosphorylation of 45 kDa protein increased by NAc-OCPC were inhibited by genistein and herbimycin A, the inhibitors of protein tyrosine kinase, but were rather enhanced by staurosporine, an inhibitor of protein kinase C.

A new metabolite of propargylglycine, gamma-glutamylpropargylglycylglycine, in liver of D,L-propargylglycine-administered rats

A new metabolite of propargylglycine (2-amino-4-pentynoic acid, a natural and synthetic inhibitor of cystathionine gamma-lyase) was isolated from liver of rats intraperitoneally administered D,L-propargylglycine with ion-exchange chromatography, and identified as a glutathione analogue, N-[N-gamma-glutamyl(propargylglycyl)]glycine (gamma-Glu-PPG-Gly), by fast-atom-bombardment-mass spectrometry and reactions of the compound including acid hydrolysis, carboxypeptidase reaction, and gamma-glutamyltranspeptidase reaction. The content of gamma-Glu-PPG-Gly in rat liver increased dose-dependently with the increase of D,L-propargylglycine. When the dose of D,L-propargylglycine was 50 mg/kg of body weight, the increase of gamma-Glu-PPG-Gly was proportional to the time after the administration of D,L-propargylglycine, up to 8 h, and then gradually decreased to about 50% of the maximum at 24 h, where the maximum level of gamma-Glu-PPG-Gly at 8 h was 1.15 +/- 0.08 micromol/g of liver. The propargylglycine moiety of gamma-Glu-PPG-Gly in rat liver at 14 h after the administration of D,L-propargylglycine corresponded to 2-7% of the propargylglycine administered when the dose of D,L-propargylglycine was 3.125-200 mg/kg of body weight. The present results indicate that gamma-Glu-PPG-Gly is a major intermediate of propargylglycine metabolism in rat liver. The structural resemblance between glutathione and gamma-Glu-PPG-Gly suggests a possible involvement of propargylglycine and gamma-Glu-PPG-Gly as cysteine and glutathione analogues, respectively, in sulfur amino-acid metabolism.

L-cysteine metabolism in guinea pig and rat tissues

Rhodanese, gamma-cystathionase and 3-mercaptopyruvate sulfurtransferase activities were examined in guinea pig and rat liver, kidney and brain. In the liver of both species rhodanese showed the same high range of activity but in guinea pig kidney and brain a slightly lower level was determined than that in corresponding rat tissues. The 3-mercaptopyruvate sulfurtransferase and gamma-cystathionase activities in all the investigated tissues of guinea pig were significantly lower than those in rat. The sulfane sulfur pool, a source of sulfur transferred by rhodanese, can be augmented in vitro in guinea pig liver, but not in rat liver when 3-mercaptolactate-cysteine disulfide is used as a substrate of gamma-cystathionase.

Spectrophotometric determination of hydrogen peroxide: catalase activity and rates of hydrogen peroxide removal by erythrocytes

A new method of hydrogen peroxide determination for the measurement of catalase activity and rates of hydrogen peroxide removal by erythrocytes was described. Hydrogen peroxide was determined by converting it to the indamine dye with a water-soluble ironporphyrin and measuring the absorbance at 590 nm. This method was applied to the assay of catalase in hemolysates from human, rat and mouse blood. The activities obtained were in agreement with those obtained by other methods including UV method. The present method was also applied to the determination of rates of hydrogen peroxide removal by intact erythrocytes from human subjects, rats and mice. Data suggested that normal erythrocytes have substantial capacity to remove extracellular hydrogen peroxide. From the measurement of catalase activity in erythrocytes treated with 3-amino-1,2,4-triazole and rates of hydrogen peroxide removal by the erythrocytes, it is deduced that rate constants related to the hemoglobin content (k/g Hb) for hydrogen peroxide removal by catalase in normal and acatalasemic erythrocytes are 42.0 +/- 6.0 and 8.0 +/- 3.0, respectively.

Isolation and characterization of N-acetyl-S-[2-carboxy-1-(1 H-imidazol-4-yl) ethyl]-L-cysteine, a new metabolite of histidine, from normal human urine and its formation from S-[2-carboxy-1-(1 H-imidazol-4-yl) ethyl]-L-cysteine

N-Acetyl-S-[2-carboxy-1-(1 H-imidazol-4-yl)ethyl]-L-cysteine (I), a new imidazole compound with a sulfur-containing side chain, was isolated from normal human urine by ion-exchange column chromatography, and characterized by physicochemical analyses involving 1H-NMR spectrometry, mass spectrometry and high-voltage paper electrophoresis as well as chemical synthesis. Approximately five milligrams of crystals of the compound were obtained from 450 litres of the urine. Compound I was synthesized by the addition of N-acetyl-L-cysteine to urocanic acid. The compound was also formed by incubation of S-[2-carboxy-1-(1 H-imidazol-4-yl)ethyl]-L-cysteine (II) with acetyl-CoA in the use of rat kidney or liver homogenate as an enzyme source in a Tris buffer at pH 7.4. Rat brain and spleen homogenates were the less or no effective preparations as the enzyme source. On the other hand, little N-acetylation of a diastereomer of compound II occurred in enzymatic reactions with rat tissue homogenates. Compound I was degraded to compound II by rat kidney or liver homogenate. These results suggest that compound I is a new N-acetylated metabolite of compound II, a compound previously found in human urine, and that the acetylating enzyme recognizes stereoisomerism of asymmetric carbon atoms on the molecule of compound II. These findings support an alternative pathway of L-histidine catabolism initiated by the adduction of glutathione and/or cysteine to urocanic acid, the first catabolite of histidine.

Protein disulfide isomerase-catalyzed renaturation of ribonuclease A modified by S-thiolation with glutathione and cysteine

Renaturation of modified ribonuclease A by protein disulfide isomerase was studied. The renaturation rate of fully S-thiolated ribonuclease A with glutathione, namely, ribonuclease A-glutathione mixed disulfide (RNase-SG) containing 8 moles of glutathione per mole of ribonuclease A (RNase-SG8), by protein disulfied isomerase (PDI) was more than three times faster than those of fully S-thiolated RNase with L-cysteine and scrambled ribonuclease A. Renaturation of RNase-SG species containing 7 or less glutathione was slower than that of RNase-SG8. These data seems to favor the hypothesis that S-thiolation of nascent proteins with glutathione may occur in the folding process during protein synthesis. The applicability of the present method consisted of chemical S-thiolation and PDI-catalyzed renaturation to the in vitro folding of recombinant cysteine-containing proteins is discussed.

Purification of a novel serpin-like protein from bovine brain

We purified a novel serine proteinase inhibitor (serpin)-like protein from the bovine brain and named it B-43 from its molecular mass, 43 kDa. A cleaved peptide from B-43 was copurified with the native B-43. Partial amino acid sequencing of the purified B-43 showed that this protein was homologous to glia-derived nexin/protease nexin-1 (GDN/PN-1), plasminogen activator inhibitor 2, leukocyte elastase inhibitor (LEI) and placental thrombin inhibitor (PTI) among the serpins. Although B-43 had a similar amino acid composition to these serpins, the biochemical features of B-43 were different from them. B-43 did not form sodium dodecyl sulfate (SDS)-resistant serpin-proteinase complexes with thrombin, urokinase, pancreatic elastase and plasmin, suggesting that these proteinases were not the targets of B-43. In contrast to GDN/PN-1, B-43 did not have an affinity for heparin. B-43, having different biochemical properties from GDN/PN-1, appears to be an additional serpin expressed in the brain.

Increase in cystathionine content in rat liver mitochondria after D,L-propargylglycine administration

Intraperitoneal administration of D,L-propargylglycine to rats resulted in an increase in the cystathionine content of whole liver and liver mitochondria. Cystathionine in mitochondria was identified by amino acid analysis, thin layer chromatography, high-voltage paper electrophoresis and liquid chromatography-mass spectrometry. The cystathionine content of whole liver was 5.37 ± 1.59µmol per g of fresh liver at 14 h after the administration of 50 mg of D,L-propargylglycine per kg of body weight, while 0.07 ± 0.02µmol of cystathionine per g of fresh liver was detected in the control rats. The cystathionine content of liver mitochondria from both groups of rats was 9.40 ± 1.20 and 0.19 ± 0.04 nmol of cystathionine per mg of protein, respectively. The mitochondrial cystathionine increased dose-dependently with the increase of D,L-propargylglycine administered. The increase was proportional to the time after the administration up to 12 h, and then decreased. The increase of cystathionine in the liver mitochondria was linearly proportional to that in the whole liver. These results suggest that cystathionine in liver mitochondria is in an equilibrium with that in the cytosol.

A method for determination of total glutathione and total cysteine as S-carboxymethyl derivatives by using an amino acid analyzer, and its application to samples from rat liver, kidney and blood after intraperitoneal administration of 2-(4-carboxy-D-gluco-tetrahydroxybutyl)thiazolidine-4-carboxylic acid

The effects of intraperitoneal administration of 2-(4-carboxy-D-gluco-tetrahydroxybutyl)thiazolidine-4-carboxylic acid (CGUA), a cysteine derivative conjugated with glucuronic acid, on total glutathione and total cysteine contents in rat tissues were investigated. Total glutathione (GSH and GSSG) and total cysteine (cysteine and cystine) were determined by a new method consisting of preparation of S-carboxymethylglutathione (CMSG) and S-carboxymethylcysteine (CMC), respectively, and subsequent analyses with an amino acid analyzer. CGUA was determined by a coloration method employing an acidic ninhydrin reagent. Total cysteine contents in liver, kidney and plasma rapidly increased to 2.3, 2.7 and 6.5 times the levels of the controls, respectively, after CGUA administration at a dose of 5 mmol/kg of body weight. Total glutathione content did not change significantly in the liver or blood except for the kidney with a significant increase during the first 1-h period after administration. CGUA content increased markedly in these tissues, especially in the kidney, and 30% of administered CGUA was excreted in urine within 2h. These results indicate that CGUA is converted into cysteine in vivo, suggesting the usefulness of this compound for protection of the kidney and the liver.

Identification of N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine in the urine of a patient with cystathioninuria using LC/APCI-MS

A new cystathionine metabolite has been identified in the urine of a patient with cystathioninuria using liquid chromatography-mass spectrometry with an atmospheric pressure chemical ionization interface system (LC/APCI-MS). By this method a very intense quasi-molecular ion was observed as a base peak of synthetic N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine (NAc-OCPC). The quasimolecular ion [M + H]+ of NAc-OCPC observed in the urine of a patient with cystathioninuria was the same as that of the authentic compound (m/z 264). The retention time and Rf value on paper chromatography of the synthetic compound were the same as those of the urinary compound from the patient with cystathioninuria. From these results, this new cystathionine metabolite was identified as N-acetyl-S-(3-oxo-3-carboxy-n-propyl)cysteine.

High-performance liquid chromatographic determination of hypotaurine and taurine after conversion to 4-dimethylaminoazobenzene-4'-sulfonyl derivatives and its application to the urine of cysteine-administered rats

A method for the determination of urinary hypotaurine and taurine for the purpose of studying hypotaurine-taurine status in mammals is described. Hypotaurine and taurine were converted into 4-dimethylaminoazobenzene-4'-sulfonyl (dabsyl) derivatives under conditions minimizing hypotaurine oxidation. The dabsylhypotaurine and dabsyltaurine formed were determined by reversed-phase HPLC. Average excretions of taurine and hypotaurine in rat urine were 270.5 and 2.5 mumol/kg body mass per day, respectively. After intraperitoneal injection of 5 mmol of L-cysteine/kg body mass, the increased excretions of taurine and hypotaurine corresponded to 22.1 and 2.5%, respectively, of L-cysteine administered, indicating that hypotaurine production exceeded the capacity of hypotaurine oxidation in vivo.

High-performance liquid chromatographic determination of taurine and hypotaurine using 3,5-dinitrobenzoyl chloride as derivatizing reagent

A method for the determination of taurine and hypotaurine in biological samples involving the preparation of their 3,5-dinitrobenzoyl derivatives followed by HPLC was established. Taurine and hypotaurine in aqueous media were reacted with 3,5-dinitrobenzoyl chloride in the presence of triethylamine to prepare 3,5-dinitrobenzoyl derivatives. These derivatives were separated on a C18 reversed-phase column and detected by recording the absorbance at 254 nm. Derivatives of taurine and hypotaurine were obtained in yields of 91.4 +/- 3.3 and 85.6 +/- 2.6%, respectively. The calibration graphs for taurine and hypotaurine were linear between 2.5 and 500 microM with correlation coefficients of 0.999. The method was applied to the determination of taurine and hypotaurine in human and rat urine and blood and in rat liver and heart.

Isolation of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-3-thiolactic acid, a new metabolite of histidine, from normal human urine and its formation from S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]cysteine

S-[2-Carboxy-1-(1H-imidazol-4-yl)ethyl]-3-thiolactic acid (CIE-TL), a novel imidazole compound with a sulphur-containing side chain, was isolated from normal human urine by ion-exchange column chromatography, and characterized by physicochemical analyses involving m.s., i.r. spectrophotometry, high-voltage paper electrophoresis and elemental analysis as well as chemical synthesis. CIE-TL was synthesized by the reaction of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]cysteine (CIE-Cys) with NaNO2 in HCl. CIE-TL was also formed during enzymic degradation of CIE-Cys by rat liver or kidney homogenate in a phosphate buffer, possibly via the metabolic intermediate S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]-3-thiopyruvic acid, and this was accompanied by the formation of 3-[(carboxymethyl)thio]-3-(1H-imidazol-4-yl)propanoic acid, a compound previously found in human urine [Kinuta, Yao, Masuoka, Ohta, Teraoka and Ubuka (1991) Biochem. J. 275, 617-621]. These results suggest that CIE-Cys [Kinuta, Ubuka, Yao, Futani, Fujiwara and Kurozumi (1992) Biochem. J. 283, 39-40] is a physiological precursor of the urinary compounds and that L-histidine is metabolized in part via an alternative pathway initiated by the adduction of natural thiol compounds such as cysteine and GSH to urocanic acid, the first catabolite of histidine.

Preparation and characterization of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]glutathione and its derivatives as proposed precursors of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]cysteine, a compound found in human urine

Formation of 3-[(carboxymethyl)thio]-3-(1H-imidazol-4-yl)propanoic acid (I) and S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]cysteine (II), compounds found in human urine, has been demonstrated by enzymatic degradation of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]glutathione (III). Compound (III) was chemically synthesized in 72% yield by incubating the reaction mixture of trans-urocanic acid and 3-fold excess GSH at 65 degrees C for 1 wk, which was accompanied by formation of N-(S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]cysteinyl)glycine (IV) in 15% yield. S-[2-Carboxy-1-(1H-imidazol-4-yl)ethyl]-N-gamma-glutamylcysteine (V) was produced by partial hydrolysis of compound (III) in HCl. The synthesized compounds were characterized mainly by fast-atom bombardment mass spectrometry and high-voltage paper electrophoresis as well as chemical degradation. Incubation of compound (III) with rat kidney homogenate in a Tris buffer (pH 8), formed compound (II) in 80% yield possibly via compound (IV). Yield of compound (II) was increased by adding glycylglycine to the reaction mixture. However, little degradation of compound (III) occurred in the use of rat liver, brain, heart or spleen homogenate as the enzyme source. Compound (II) was further metabolized to compound (I) by incubation with rat kidney homogenate in a phosphate buffer of pH 7.4. From these results, we suggest that the urinary compounds are products of enzymatic degradation of compound (III) and that GSH may participate in the metabolism of urocanic acid, the first catabolite of L-histidine.

Assay of sialidase activity using ion-exchange chromatography and acidic ninhydrin reaction

A new assay method for sialidase (EC 3.2.1.18) activity using ion-exchange chromatography and acidic ninhydrin reaction has been developed. Fetuin, 4-methylumbelliferyl-N-acetylneuraminic acid (MUB-NANA), gangliosides and N-acetylneuramin-lactose were examined as substrates. Free sialic acid liberated from these substrates by sialidase reaction was isolated with a Dowex 1-X8 column (trifluoroacetate form, 1.5 cm x 0.5 cm I.D.) and determined by acidic ninhydrin reaction. Among the substrates tested, MUB-NANA was the best in the present method, N-Acetylneuramin-lactose could not be used as the substrate, because it was not separated from liberated sialic acid under the conditions used. The recovery of N-acetylneuraminic acid was above 88%, and the sensitivity of the method was 20 nmol in 300 microliters of the reaction mixture. The method was applied to the sialidase assay during its purification from rat skeletal muscle, and a Michaelis constant of 1.15 mM was obtained with MUB-NANA as the substrate. The method using the acidic ninhydrin reaction was simple and exhibited good reproducibility.

Isolation of S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]cysteine from human urine

S-[2-Carboxy-1-(1H-imidazol-4-yl)ethyl]cysteine (I), a proposed precursor of 3-[(carboxymethyl)thio]-3-(1H-imidazol-4-yl)propanoic acid [Kinuta, Yao, Masuoka, Ohta, Teraoka & Ubuka (1991) Biochem. J. 275, 617-721], was isolated from healthy human urine by using ion-exchange column chromatography. Identification of the isolated compound with compound (I) was performed by physicochemical analyses involving i.r., m.s. and n.m.r. spectrometries as well as high-voltage paper electrophoresis, t.l.c. and paper chromatography. Compound (I) was synthesized in 80% yield by incubation of a reaction mixture containing trans-urocanic acid and 3-fold excess of cysteine at 70-75 degrees C. From these results we suggest that natural thiol compounds such as cysteine and GSH participate in the metabolism of urocanic acid, a key metabolite of L-histidine.

Isolation and characterization of 3-[(carboxymethyl)thio]-3-(1H-imidazol-4-yl)propanoic acid from human urine and preparation of its proposed precursor, S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]cysteine

3-[(Carboxymethyl)thio]-3-(1H-imidazol-4-yl)propanoic acid (I) was isolated from healthy human urine by using ion-exchange column chromatography, and characterized by physicochemical analyses involving i.r., m.s. and n.m.r. spectrometries as well as chemical synthesis. The urinary content was 0.04-0.07 mumol/l. Compound (I) was synthesized by the addition of mercaptoacetic acid to urocanic acid. In order to establish the origin of the compound. S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]cysteine (II) and S-[2-carboxy-1-(1H-imidazol-4-yl)ethyl]glutathione (III) were produced by similar reactions of urocanic acid with cysteine and GSH respectively. The yield of compound (II) was markedly increased by sunlight irradiation of the reaction mixture or by the use of cis-urocanic acid rather than the trans isomer. Incubation of compound (II) with rat liver homogenate in a phosphate buffer, pH 7.40, formed a major and some minor products of enzymic degradation, one of which was identified with compound (I). Exposure of rats to the sunlight for 2 days resulted in increase of the epidermal content of trans-urocanic acid from the normal value of 0.38 to 1.70 micrograms/mg wet wt. of skin, accompanied by formation de novo of the epidermal cis isomer. After sunlight irradiation, the content of the trans isomer decreased at a constant rate of 0.03 micrograms/mg wet wt. of skin per day, whereas the cis isomer was eliminated more quickly, having a phase of rapid decrease in the early period. From these results we suggest that compound (I) may participate in the metabolism of urocanic acid and natural thiol compounds such as cysteine and GSH.

Excretion of 3-mercaptolactate-cysteine mixed disulfide, sulfate and taurine in human urine before and after oral administration of sulfur-containing amino acids

The excretion of 3-mercaptolactate-cysteine mixed disulfide [S-(2-hydroxy-2-carboxyethylthio)-L-cysteine, HCETC], sulfate and taurine in the urine of normal adults was investigated before and after oral administration of L-cysteine and related sulfur-containing amino acids. Before the loading of amino acids, the excretion (mean +/- SD) per kg of body weight per day of HCETC, free sulfate and taurine was 0.096 +/- 0.042, 305.7 +/- 66.1 and 31.9 +/- 8.7 mumols, respectively. After the loading of L-cysteine (800 mumols/kg of body weight), the average excretion in the 24-h urine of HCETC increased 2-fold and that of taurine increased 1.6-fold. The average excretion of free sulfate after the L-cysteine loading was 989.4 +/- 145.1 and 388.8 +/- 51.6 mumols/kg per day in the first and second 24-h urine, respectively, indicating that the sulfur corresponding to 85% of the L-cysteine loaded was excreted as free sulfate in 24 h. Administration of L-cystine (400 mumols/kg) resulted in similar results. The increase in HCETC after L-cysteine or L-cystine administration indicates that L-cysteine is metabolized in part through the transamination pathway (3-mercaptopyruvate pathway) and that an equilibrium exists between the intake and excretion of sulfur in humans.

Tissue contents and urinary excretion of taurine after administration of L-cysteine and L-2-oxothiazolidine-4-carboxylate to rats

Tissue contents and urinary excretion of taurine were studied in rats after the administration of L-cysteine and its derivatives. Average taurine content in the liver of rats fed a 25% casein diet for 7 days increased 2-fold 2h after the intraperitoneal administration of 5 mmol of L-cysteine per kg of body weight, whereas that in rats fed a 5% casein diet for 2 days increased only slightly. The difference in the liver taurine contents between these two groups was discussed in relation to cysteine dioxygenase. Taurine contents in the heart, brain and blood did not differ significantly between these two groups or between the control and the group of rats which received L-cysteine. The increase in liver taurine concentrations after L-cysteine administration was much higher than that after L-cystine administration, suggesting a difference in their absorption. The intraperitoneal administration of 5 mmol/kg of L-2-oxothiazolidine-4-carboxylate (OTCA) resulted in a 3-fold increase in liver taurine content. The average increase in taurine excretion in the 24-h urine after OTCA administration corresponded to about 6.0% and that in the next 24-h urine to about 2.6% of OTCA administered, suggesting that nearly 10% of OTCA was metabolized to taurine and excreted in the urine.

Visualization of sialoglycoproteins in polyacrylamide gels by acidic ninhydrin reaction

A new method for staining sialoglycoproteins in polyacrylamide gel after disc electrophoresis is described. The method utilizes the reaction of sialic acids with an acidic ninhydrin reagent which yields a stable color with an absorption maximum at 470 nm. After electrophoresis, the polyacrylamide gel is placed in a test tube and heated with 5 ml of the acidic ninhydrin reagent for 10 min in a boiling water bath. Sialoglycoproteins are detected as brown bands. No additional procedure such as destaining is necessary. When 20 micrograms fetuin, a sialoglycoprotein, per gel is applied, the band remains visible for at least 2 h. Stained gel can be scanned with a gel scanner at 470 nm. When the stained gel was dried on a sheet of polypropylene filter, the color was stable for at least one month. The present method is superior to the method using Stains-all (3,3'-diethyl-9-methyl-4,5,4',5'-dibenzothiacarbocyanine) in specificity and simplicity for the detection of sialoglycoproteins.

Formation of sulfate from L-cysteine in rat liver mitochondria

Formation of sulfate in rat liver mitochondria was studied. About 0.1 mumol of sulfate was formed in mitochondria from 1 g of liver in 60 min when 10 mM L-cysteine was used as the substrate. Addition of either 10 mM 2-oxoglutarate or 10 mM glutathione to this system increased sulfate formation 3 to 4 times. The addition of both 2-oxoglutarate and glutathione resulted in a 20-fold increase in sulfate formation. Sulfate formation in the presence of 5 mM L-cysteine was 58% of that with 10 mM L-cysteine. L-Cysteine-glutathione mixed disulfide was not a good substrate, indicating that this mixed disulfide was not an intermediate of sulfate formation in the present system. Incubation of 3-mercaptopyruvate with rat liver mitochondria also resulted in sulfate formation, and the addition of glutathione accelerated it. Formation of sulfite and thiosulfate was also detected. These results indicate that sulfate is produced in mitochondria, at least in part, from L-cysteine through the transamination pathway (3-mercaptopyruvate pathway).

Determination of hypotaurine and taurine in blood plasma of rats after the administration of L-cysteine

A method for the simultaneous determination of hypotaurine and taurine was developed. The method consisted of the elimination of urea, which interfered with the determination of hypotaurine, by immobilized urease, and determination of hypotaurine and taurine with an amino acid analyzer. The analyzer equipped with a cation-exchange column was operated at 32 degrees C with 0.2 M sodium citrate buffer, pH 2.8. Using this method, the dynamics of hypotaurine and taurine in blood plasma of rats was studied after the intraperitoneal injection of L-cysteine. The concentration of cysteine reached the maximum 1 h after L-cysteine loading. The concentration of hypotaurine and taurine increased in parallel and reached the maximum 2 h after L-cysteine loading. These changes seem to indicate the precursor-product relationship of these substances and the rapid conversion of hypotaurine to taurine in vivo.

Preparation of a volatile derivative of taurine and application to gas chromatographic determination of urinary taurine

A new volatile derivative of taurine, N-isobutoxycarbonyltaurine methyl ester (methyl 2-(N-isobutoxycarbonylamino)ethanesulfonate), was prepared by a three-step procedure for the gas chromatographic determination of taurine in urine. First, taurine was converted to its silver salt by reaction with silver oxide; next the silver salt was reacted with isobutyl chloroformate to form the N-isobutoxycarbonyl derivative, and finally the derivative was reacted with methyl iodide to form N-isobutoxycarbonyltaurine methyl ester. The volatile derivative was analyzed by gas chromatography using a column of 3% OV-101 on Chromosorb W. When methyl 3-(N-isobutoxycarbonylamino) propanesulfonate was used as an internal standard, the calibration curve was linear between 0.5 and 5.0 mumol of taurine/ml and showed a good reproducibility. This method was applied to the determination of taurine in human urine. Recovery was 98.6 +/- 5.2%, when 1.25 to 5.0 mumol/ml of taurine was added to human urine.

Sulfate and taurine excretion in rats after L-cysteine administration

Excretion of sulfate and taurine, two major metabolites of sulfur, was examined in rats to study the nutritional status of sulfur metabolism in the mammals. Rats maintained on a conventional laboratory diet excreted 1.83 +/- 0.14 mmol of free sulfate and 229.0 +/- 75.3 mumol of taurine/kg of body weight per day. When the diet was changed to a synthetic 25% casein diet, the taurine excretion decreased to 15% of the previous daily excretion, but sulfate excretion decreased only slightly. These decreased levels returned to the original levels when 5 mmol of L-cysteine/kg of body weight was administered into the stomach through a catheter. One week after the first L-cysteine administration, when sulfate and taurine excretion had returned to the original levels, 5 mmol of L-cysteine/kg of body weight was administered likewise. The rats excreted sulfur corresponding to about 95% of L-cysteine administered in the form of free sulfate and taurine within a few days following L-cysteine administration, and sulfate excretion was 3.5 times more than taurine excretion. These results seem to suggest that, in rats, sulfur metabolism is in a state of equilibrium and that sulfate is formed preferentially to taurine.