Purification and Properties of 3-Hydroxyanthranilic Acid Oxidase

The relationship between postmortem interval and protein changes in mice

Postmortem interval (PMI) estimation is important for forensic pathological autopsy. It has been reported that there is a correlation between certain protein changes in cadavers and PMI. However, no specific protein(s) has been used to determine the PMI so far. In this study, the total protein contents of mouse liver and spleen at different time of death were measured. The data showed that they were negatively correlated with the PMI. The degradation of β-actin was found to be positively correlated with the PMI in the liver. Additionally, proteomic technique was used to study the changes of protein expression related to PMI in the liver of mice. By using Two-dimensional electrophoresis, the expressions of four proteins were found to be significantly decreased and those of other three proteins were unchanged with the increase of PMI. Among the seven proteins, six were identified with peptide mass fingerprinting using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The three altered proteins were SBP2, ENOA, ALDH2 and three unchanged ones were 3HAO, TPIS, CATA, respectively. In the future, those unchanged proteins could be used as internal references to more accurately and reliably infer the time of death by assessing the level of changed proteins.

Metalloproteomic Strategies for Identifying Proteins as Biomarkers of Mercury Exposure in Serrasalmus rhombeus from the Amazon Region

This manuscript describes the results of a metalloproteomic study of mercury in samples of muscle and liver tissue of the species Serrasalmus rhombeus, popularly known as black piranha and characterised as the most voracious and aggressive predator in the Brazilian Amazon. The metalloproteomic study involved using two-dimensional electrophoresis (2D PAGE) to fractionate the proteome of the muscle and liver tissue samples, along with atomic absorption spectrometry in a graphite furnace (GFAAS) to identify mercury associated with protein SPOTs and mass spectrometry with electrospray ionisation (ESI-MS/MS) to characterise the mercury-binding proteins. The protein SPOTs characterised showed concentrations in the order of 156 mg kg^-1, which ranks as the highest concentrations of mercury determined so far in metalloproteomic studies involving fish species in the Amazon region. Based on FASTA sequences of proteins characterised by ESI-MS/MS, bioinformatics studies were performed that allowed identifying nine proteins with characteristics of biomarkers of mercury exposure. Of those proteins, glutathione peroxidase stands out as an enzyme of great importance in the antioxidant defence of organisms subjected to oxidative stress caused by xenobiotics.

Extreme pathway analysis reveals the organizing rules of metabolic regulation

Cellular systems shift metabolic states by adjusting gene expression and enzyme activities to adapt to physiological and environmental changes. Biochemical and genetic studies are identifying how metabolic regulation affects the selection of metabolic phenotypes. However, how metabolism influences its regulatory architecture still remains unexplored. We present a new method of extreme pathway analysis (the minimal set of conically independent metabolic pathways) to deduce regulatory structures from pure pathway information. Applying our method to metabolic networks of human red blood cells and Escherichia coli, we shed light on how metabolic regulation are organized by showing which reactions within metabolic networks are more prone to transcriptional or allosteric regulation. Applied to a human genome-scale metabolic system, our method detects disease-associated reactions. Thus, our study deepens the understanding of the organizing principle of cellular metabolic regulation and may contribute to metabolic engineering, synthetic biology, and disease treatment.

A mathematical model of tryptophan metabolism via the kynurenine pathway provides insights into the effects of vitamin B-6 deficiency, tryptophan loading, and induction of tryptophan 2,3-dioxygenase on tryptophan metabolites

Vitamin B-6 deficiency is associated with impaired tryptophan metabolism because of the coenzyme role of pyridoxal 5'-phosphate (PLP) for kynureninase and kynurenine aminotransferase. To investigate the underlying mechanism, we developed a mathematical model of tryptophan metabolism via the kynurenine pathway. The model includes mammalian data on enzyme kinetics and tryptophan transport from the intestinal lumen to liver, muscle, and brain. Regulatory mechanisms and inhibition of relevant enzymes were included. We simulated the effects of graded reduction in cellular PLP concentration, tryptophan loads and induction of tryptophan 2,3-dioxygenase (TDO) on metabolite profiles and urinary excretion. The model predictions matched experimental data and provided clarification of the response of metabolites in various extents of vitamin B-6 deficiency. We found that moderate deficiency yielded increased 3-hydroxykynurenine and a decrease in kynurenic acid and anthranilic acid. More severe deficiency also yielded an increase in kynurenine and xanthurenic acid and more pronounced effects on the other metabolites. Tryptophan load simulations with and without vitamin B-6 deficiency showed altered metabolite concentrations consistent with published data. Induction of TDO caused an increase in all metabolites, and TDO induction together with a simulated vitamin B-6 deficiency, as has been reported in oral contraceptive users, yielded increases in kynurenine, 3-hydroxykynurenine, and xanthurenic acid and decreases in kynurenic acid and anthranilic acid. These results show that the model successfully simulated tryptophan metabolism via the kynurenine pathway and can be used to complement experimental investigations.

Structure and function of atypically coordinated enzymatic mononuclear non-heme-Fe(II) centers

Mononuclear, non-heme-Fe(II) centers are key structures in O₂ metabolism and catalyze an impressive variety of enzymatic reactions. While most are bound via two histidines and a carboxylate, some show a different organization. A short overview of atypically coordinated O₂ dependent mononuclear-non-heme-Fe(II) centers is presented here Enzymes with 2-His, 3-His, 3-His-carboxylate and 4-His bound Fe(II) centers are discussed with a focus on their reactivity, metal ion promiscuity and recent progress in the elucidation of their enzymatic mechanisms. Observations concerning these and classically coordinated Fe(II) centers are used to understand the impact of the metal binding motif on catalysis.

Effects of oxygen on kynurenine-3-monooxygenase activity

Kynurenine-3-monooxygenase (KM), the third enzyme in the kynurenine (KYN) pathway from tryptophan to quinolinic acid (QA), is a monooxygenase requiring oxygen, NADPH and FAD for the catalytic oxidation of L-kynurenine to 3-hydroxykynurenine and water. KM is innately low in the brain and similar in activity to indoleamine oxidase, the rate-limiting pathway enzyme. Accumulation in the CNS of QA, a known excitotoxin, is proposed to cause convulsions in several pathologies. Thus, we theorized that hyperbaric oxygen (HBO) induced convulsions arise from increased QA via oxygen K, effects on this pathway [Brown OR, Draczynska-Lusiak. Oxygen activation and inactivation of quinolinate-producing and iron-requiring 3-hydroxyanthranilic acid oxidase: a role in hyperbaric oxygen-induced convulsions? Redox Report 1995; 1: 383-385]. To complement prior studies on the effects of oxygen on pathway enzymes, in this paper we report the effects of oxygen on KM. Brain and liver KM enzyme are not known to be identical, and some systemically-produced KYN pathway intermediates can permeate the brain and might stimulate the brain pathway. Thus, KM from both brain and liver was assayed at various oxygen substrate concentrations to evaluate, in vitro, the potential effects of increases in oxygen, as would occur in mammals breathing therapeutic and convulsive HBO. In crude tissue extracts, KM was not activated during incubation in HBO up to 6 atm. The effects of oxygen as substrate on brain and liver KM activity was nearly identical: activity was nil at zero oxygen with an apparent oxygen Km of 20-22 microM. Maximum KM activity occurred at about 1000 microM oxygen and decreased slightly to plateau from 2000 to 8000 microM oxygen. This compares to approximately 30-40 microM oxygen typically reported for brain tissue of humans or rats breathing air, and an unknown but surely much lower value (perhaps below 1 microM) intracellularly at the site of KM. Thus HBO, as used therapeutically and at convulsive pressures, likely stimulates flux through the KM-catalyzed step of the KYN pathway in liver and in brain and could increase brain QA, by Km effects on brain KM, or via increased KM pathway intermediates produced systemically (in liver) and transported into the brain.

Tryptophan metabolism and brain function: focus on kynurenine and other indole metabolites

The synthesis of NAD (or NADP) from tryptophan involves a series of enzymes and the formation of a number of intermediates which are collectively called 'kynurenines.' In the late 1970s and early 1980s, it became clear that intraventricular administration of several 'kynurenines' could cause convulsions and that one of the 'kynurenines,' quinolinic acid, was an agonist of a sub-population of NMDA receptors and caused excitotoxic neuronal death. A related metabolite, kynurenic acid, could, on the other hand, reduce excitotoxin-induced neuronal death by antagonising ionotropic glutamate receptors. Since then, modifications in quinolinic and kynurenic acid synthesis have been proposed as a pathogenetic mechanism in Huntington's chorea and epilepsy. It was subsequently shown that a robust activation of the kynurenine pathway and a large accumulation of quinolinic acid in the central nervous system occurred in several inflammatory neurological disorders. More recently, it has been shown that 3OH-kynurenine or 3OH-anthranilic acid, two other kynurenine metabolites, may cause either apoptotic or necrotic neuronal death in cultures and that inhibitors of kynurenine hydroxylase may reduce neuronal death in in vitro and in vivo models of brain ischaemia or excitotoxicity. Finally, it has been reported that indole metabolites, indirectly linked to the kynurenine pathway, are able to modify neuronal function and animal behaviour by interacting with voltage-dependent Na+ channels. Oxindole, one of these metabolites, has sedative and anticonvulsant properties and accumulates in the blood and brain when liver function is impaired. In conclusion, a number of metabolites affecting brain function originate from tryptophan metabolism. Selective inhibitors of their forming enzymes may be useful to understand their role in physiology or as therapeutic agents in pathology.

Effects of oxygen on 3-hydroxyanthranilate oxidase of the kynurenine pathway

Iron containing 3-Hydroxyanthranilate oxidase (3HAO) converts 3-hydroxyanthranilate (3HAA) and dioxygen into a precursor which spontaneously converts to quinolinic acid (QA). 3HAO participates in de novo biosynthesis of NAD in mammalian kidney and liver, and it is present in low concentrations in brain where its function is controversial. However, QA increases in spinal fluid and is associated with convulsions in AIDS dementia, Huntington's disease, and CNS inflammation. QA is a known N-methyl, D-aspartate receptor agonist and excitotoxin that causes convulsions when injected into the brain. Hyperbaric oxygen (HBO) also causes convulsions and we investigated the interrelationships among the stimulating and toxic effects of oxygen and the role of iron in vitro using rat liver enzyme which is reported to be identical to brain enzyme and is more abundant. 3HAO requires dioxygen as a substrate but it was inactivated approximately 40% by 5.2 atm HBO in vitro in 15 min. The apparent Km was 2.6 x 10(-4) M for oxygen and 5 x 10(-5) M for 3HAA, and these values did not change for enzyme that was half-inactivated by HBO oxygen. Thus, oxygen-inactivation appears to be all-or-none for individual enzyme molecules. Freshly prepared enzyme was activated about 3-fold by incubation with acidic iron. Iron-staining of 3HAO, separated by gel electrophoresis after partial purification by FPLC, showed that loss of iron and loss of enzyme activity during HBO exposure were correlated. The apparent oxygen Km of 3HAO is far higher than the oxygen concentration in brain cells. Thus, 3HAO is capable of being stimulated initially in animals breathing HBO, and subsequently of being inactivated with potential significance for brain QA and convulsions.

The yeast gene YJR025c encodes a 3-hydroxyanthranilic acid dioxygenase and is involved in nicotinic acid biosynthesis

We have deleted the yeast gene YJR025c and shown that this leads to an auxotrophy for nicotinic acid. The deduced protein sequence of the gene product is homologous to the human 3-hydroxyanthranilic acid dioxygenase (EC 1.13.11.6) which is part of the kynurenine pathway for the degradation of tryptophan and the biosynthesis of nicotinic acid. In cell-free extracts the 3-hydroxyanthranilic acid dioxygenase activity is proportional to the copy number of the YJR025c gene. As YJR025c encodes the yeast 3-hydroxyanthranilic acid dioxygenase, we have named this gene BNA1 for biosynthesis of nicotinic acid.

Histological and ultrastructural changes in the rat brain following systemic administration of picolinic acid

Picolinic acid was administered intraperitoneally in a dose of 30, 60, or 100 mmol, once every 24 h for 8 days. Histologically, under normal conditions as well as when picolinic acid was administered in a dose of 30 mmol the brain formations exhibited characteristic features. When picolinic acid was administered in a dose of 60 mmol or 100 mmol, the alterations were profound and developed selectively in hippocampus, being much less intense in the substantia nigra and striatum. In such cases, injuries of neuronal cell bodies were accompanied by symptoms of spongiosis. Within the hippocampus, the neuronal cell body injury was selectively restricted to the hilar and CA3 regions of stratum pyramidale. Tissue spongiosis was more intense at the granular layer, particularly within the hilus and in the mossy fiber area at CA3. Histochemically, a variable intensity of the reaction of succinic and alpha-glycerophosphate dehydrogenases was demonstrated. A decrease in their activities was observed in areas where the neuronal cell body injuries and spongiosis took place. No changes in the Ca-ATP-ase activity in brain formation after picolinic acid treatment were observed. Ultrastructurally, the changes within substantia nigra were manifested by neuronal cell bodies of the dark type and dendritic degenerations. Also less damaged neuronal cell bodies were seen. They were swollen, depleted of polyribosomes with dilated elements of RER and altered mitochondria. Some of the dendritic profiles were swollen with lucent cytoplasm. Most of the boutons in synaptic contact zones were unchanged. Most presynaptic terminals which were in junction with dark dendrites were swollen with or without crystal-like aggregates of synaptic vesicles.

Liver 3-hydroxyanthranilic acid oxygenase activity in rainbow trout (Oncorhynchus mykiss)

1. In rainbow trout, 3HAA activity was comparable with those of terrestrial animals; 3HAA:PC activity ratio suggests ineffective conversion of tryptophan to niacin. 2. Inactivation as well as reactivation under different conditions was investigated. 3. Some characteristics of the enzyme extract were studied with the aim of optimizing assay in fish.

Rat 3-hydroxyanthranilic acid oxygenase: purification from the liver and immunocytochemical localization in the brain

3-Hydroxyanthranilic acid oxygenase (3HAO; EC 1.13.11.6), the biosynthetic enzyme of the endogenous excitotoxin quinolinic acid, was purified to homogeneity from rat liver and partially purified from rat brain. The pure enzyme is a single subunit protein with a molecular weight of 37-38,000. Kinetic analyses of both pure liver and partially purified brain 3HAO revealed an identical Km of 3 microM for the substrate 3-hydroxyanthranilic acid. Evidence for the identity of liver and brain 3HAO was further provided by physicochemical (electrophoretic behavior, heat sensitivity) and biochemical (pH dependency, activation by Fe2+) means. Antibodies were produced against the pure liver enzyme and the identity of liver and brain 3HAO substantiated immunologically in immunotitration and Ouchterlony double-diffusion experiments. Immunohistochemical studies using purified anti-rat 3HAO antibodies were performed on tissue sections of perfused brains and demonstrated a preferential staining of astroglial cells. Notably, the cellular localization of 3HAO in the brain appears to be in part distinct from that of quinolinic acid phosphoribosyltransferase, the catabolic enzyme of quinolinic acid. Pure rat 3HAO and its antibodies can be expected to constitute useful tools for the further elucidation of the brain's quinolinic acid system.

Synthesis of quinolinic acid by 3-hydroxyanthranilic acid oxygenase in rat brain tissue in vitro

In mammalian peripheral organs, 3-hydroxyanthranilic acid oxygenase (3HAO), catalyzing the conversion of 3-hydroxyanthranilic acid to quinolinic acid, constitutes a link in the catabolic pathway of tryptophan to NAD. Because of the possible involvement of quinolinic acid in the initiation of neurodegenerative phenomena, we examined the presence and characteristics of 3HAO in rat brain tissue. A simple and sensitive assay method, based on the use of [carboxy-14C]3-hydroxyanthranilic acid as a substrate, was developed and the enzymatic product, [14C]quinolinic acid, identified by chromatographic and biochemical means. Kinetic analysis of rat forebrain 3HAO revealed a Km of 3.6 +/- 0.5 microM for 3-hydroxyanthranilic acid and a Vmax of 73.7 +/- 9.5 pmol quinolinic acid/h/mg tissue. The enzyme showed pronounced selectivity for its substrate, since several substances structurally and metabolically related to 3-hydroxyanthranilic acid caused less than 25% inhibition of activity at 500 microM. Both the Fe2+ dependency and the distinct subcellular distribution (soluble fraction) of brain 3HAO indicated a close resemblance to 3HAO from peripheral tissues. Examination of the regional distribution in the brain demonstrated a 10-fold variation between the region of highest (olfactory bulb) and lowest (retina) 3HAO activity. The brain enzyme was present at the earliest age tested (7 days postnatum) and increased to 167% at 15 days before reaching adult levels. Enzyme activity was stable over extended periods of storage at -80 degrees C. Taken together, these data indicate that measurements of brain 3HAO may yield significant information concerning a possible role of quinolinic acid in brain function and/or dysfunction.

Biosynthesis of stizolobinic acid and stizolobic acid in higher plants. An enzyme system(s) catalyzing the conversion of dihydroxyphenylalanine into stizolobinic acid and stizolobic acid from etiolated seedlings of Stizolobium hassjoo

It was demonstrated that an enzyme system(s) extracted from etiolated seedlings of Stizolobium hassjoo catalyzed the conversion of L-dihydroxyphenylalanine into stizolobinic acid, alpha-amino-6-carboxy-2-oxo-2H-pyran-3-propionic acid, and stizolobic acid, alpha-amino-6-carboxy-2-oxo-2H-pyran-4-propionic acid, in the presence of NADP+ or NAD+ under aerobic conditions. Enzymically synthesized radioactive stizolobinic acid and stizolobic acid isolated from the reaction mixtures were purified and confirmed to have constant specific radioactivities by cocrystallization with authentic samples. Maximal activity of the enzyme preparation was obtained by using an insoluble polyphenol adsorbent (Polyclar AT) and a reducing agent (araboascorbic acid) in the extraction medium and by subsequent fractionation of the extract with ammonium sulfate followed by Sephadex G-25 gel filtration. Catalytic activity of the enzyme preparation was more unstable under aerobic condition than anaerobic. Attempts to stabilise the enzyme activity were made by the use of many substances which are known to stabilise other enzymes or expected to arrest the inactivation. Evidence is provided in this paper that the previously proposed biosynthetic pathways of stizolobinic acid and stizolobic acid from dihydroxyphenylalanine proceeded in the cell-free system from etiolated seedlings of S. hassjoo.