Immunochemical properties of D-amino-acid oxidase

Interaction of carbon nanoparticles to serum albumin: elucidation of the extent of perturbation of serum albumin conformations and thermodynamical parameters

Carbon nanoparticles continuously generated from industries and vehicles due to incomplete combustion of fuels is one of the potent causes of air pollution. The exposure of this polluted air with carbon nanoparticles, introduced into the bloodstream of animals in the course of respiration, motivated us to study their interaction with plasma proteins, bovine serum albumin and human serum albumin. Carbon nanoparticles with very small size and high purity were synthesized by dehydration of d-glucose using concentrated sulphuric acid as dehydrating agent. These were characterized by transmission electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, FTIR spectroscopy and UV-visible spectroscopy. Carbon nanoparticles-protein interactions were studied by fluorescence spectroscopy, circular dichroism spectroscopy and isothermal titration calorimetry. The fluorescence quenching constants and thermodynamic parameters such as enthalpy change (ΔH°), entropy change (ΔS°) and free energy change (ΔG°) were calculated, which indicated a strong static quenching and primary electrostatic interaction between the carbon nanoparticles and blood proteins. Circular dichroism spectra provided the information about the secondary structure alteration of the proteins in presence of carbon nanoparticles. These findings have shed light towards an understanding of the interactions between carbon nanoparticles and serum proteins which may clarify the potential risks and undesirable health effects of carbon nanoparticles, as well as the related cellular trafficking and systemic translocation.

The neurobiology of D-amino acid oxidase and its involvement in schizophrenia

D-amino acid oxidase (DAO) is a flavoenzyme that metabolizes certain D-amino acids, notably the endogenous N-methyl D-aspartate receptor (NMDAR) co-agonist, D-serine. As such, it has the potential to modulate the function of NMDAR and to contribute to the widely hypothesized involvement of NMDAR signalling in schizophrenia. Three lines of evidence now provide support for this possibility: DAO shows genetic associations with the disorder in several, although not all, studies; the expression and activity of DAO are increased in schizophrenia; and DAO inactivation in rodents produces behavioural and biochemical effects, suggestive of potential therapeutic benefits. However, several key issues remain unclear. These include the regional, cellular and subcellular localization of DAO, the physiological importance of DAO and its substrates other than D-serine, as well as the causes and consequences of elevated DAO in schizophrenia. Herein, we critically review the neurobiology of DAO, its involvement in schizophrenia, and the therapeutic value of DAO inhibition. This review also highlights issues that have a broader relevance beyond DAO itself: how should we weigh up convergent and cumulatively impressive, but individually inconclusive, pieces of evidence regarding the role that a given gene may have in the aetiology, pathophysiology and pharmacotherapy of schizophrenia?

d-Amino acid oxidase and serine racemase in human brain: normal distribution and altered expression in schizophrenia

The N-methyl-D-aspartate receptor co-agonist d-serine is synthesized by serine racemase and degraded by D-amino acid oxidase. Both D-serine and its metabolizing enzymes are implicated in N-methyl-D-aspartate receptor hypofunction thought to occur in schizophrenia. We studied D-amino acid oxidase and serine racemase immunohistochemically in several brain regions and compared their immunoreactivity and their mRNA levels in the cerebellum and dorsolateral prefrontal cortex in schizophrenia. D-Amino acid oxidase immunoreactivity was abundant in glia, especially Bergmann glia, of the cerebellum, whereas in prefrontal cortex, hippocampus and substantia nigra, it was predominantly neuronal. Serine racemase was principally glial in all regions examined and demonstrated prominent white matter staining. In schizophrenia, D-amino acid oxidase mRNA was increased in the cerebellum, and as a trend for protein. Serine racemase was increased in schizophrenia in the dorsolateral prefrontal cortex but not in cerebellum, while serine racemase mRNA was unchanged in both regions. Administration of haloperidol to rats did not significantly affect serine racemase or D-amino acid oxidase levels. These findings establish the major cell types wherein serine racemase and D-amino acid oxidase are expressed in human brain and provide some support for aberrant D-serine metabolism in schizophrenia. However, they raise further questions as to the roles of D-amino acid oxidase and serine racemase in both physiological and pathophysiological processes in the brain.

The adsorption–desorption process of bovine serum albumin on carbon nanotubes

The aim of this work is to study the adsorption-desorption process of bovine serum albumin (BSA) on carbon nanotubes (CNT) by reflectometry. The effect of the surface properties was analyzed by comparing the behavior of BSA on silica. The experiments were performed by reflectometry at different BSA concentrations, at pH 3.0, 4.8, and 7.0 and at two ionic strengths. Protein desorption was induced by either dilution with buffer or the addition of SDS. The initial adsorption rate is controlled by the attachment of BSA molecules to the surface, and strongly diminishes at pH 7. Adsorption isotherms reflect the high affinity of BSA for both sorbent surfaces and reach well-defined plateau values that depend on the pH, being the highest at pH 4.8 on CNT. Experiments performed at different ionic strengths (NaCl added) showed a less pronounced effect. Dilution does not induce desorption on either surface however, the addition of SDS removes protein only from the silica surface.

Presence of D-aspartate oxidase and free D-aspartate in amphibian (Xenopus laevis, Cynops pyrrhogaster) tissues

1. This paper is the first report on the presence of D-aspartate oxidase activity and free D-aspartate in the amphibian tissues. 2. The presence of D-aspartate oxidase activity in tissues of clawed toad (Xenopus laevis) and Japanese newt (Cynops pyrrhogaster) was demonstrated by requirements for enzyme activity, selective inhibition with meso-tartrate and substrate specificity. 3. In each animal, the highest activity was found in kidney, followed by liver and brain, and no gender difference in the specific activity was observed in each tissue. 4. A small but significant amount of D-aspartate was detected in liver and kidney, irrespective of species. 5. In the newt, there was a gender difference in the hepatic and renal content of D-aspartate and not in the D-/D+L-aspartate ratio.

Regional differences for the d-amino acid oxidase-catalysed oxidation of d-methionine in chicken small intestine

1. Enzymic oxidation of D-[1-14C]methionine (D-met) to 2-keto-4-methylthiobutanoate (KMB) has been determined using 100,000 g supernatants prepared from chicken tissue homogenates. 2. The small intestinal mucosa contains substantial oxidative activity towards D-met, which represents about one-half and one-tenth the hepatic and renal activity, respectively. 3. KMB is poorly decarboxylated and rather transaminated to L-met. 4. The specific activity for D-met oxidation in the duodenal mucosa is 1.5- and 4.0-fold than in the jejunal and ileal mucosa, respectively. 5. The intestinal D-met-oxidizing activity is dramatically altered by the D-amino acid oxidase specific inhibitor benzoate.

Immunochemical studies on Rhodotorula gracilis D-amino acid oxidase

Polyclonal antibodies were prepared from rabbit sera after immunization with holo- and apo-D-amino acid oxidase purified from R. gracilis. Both anti-holo- and anti-apoenzyme IgG fractions (as well as affinity-purified IgG) were highly specific: in blot-transfer analyses after SDS-PAGE only a 39 kDa band, corresponding to enzyme monomer, was recognized even in the partially purified yeast extract. No cross-reaction was detected with pig kidney D-amino acid oxidase. As a difference from the mammalian enzyme, yeast D-amino acid oxidase anti-holo- and anti-apoenzyme IgGs had different properties in inactivation and precipitation experiments, indicating the existence of different antigenicity sites related to the FAD-binding domain in the enzyme.

Differential effect of sunflower seed oil on hepatic and renal D-amino acid oxidase in the rat

1. The specific activity of hepatic and renal peroxisomal D-amino acid oxidase (D-AAOX) was measured in rats fed diets containing various quantities of vegetable oil. 2. Increasing the amount of dietary sunflower seed oil (SSO) from 10 to 25% (w/w) reduced the specific activity of hepatic D-AAOX by up to 30% after 10 days. 3. In both tissues, the enzyme activity was moderately decreased during the first two-day period after administration of the 25% SSO diet was begun. Unlike hepatic D-AAOX, renal D-AAOX returned to its baseline level in the kidney after the third day. 4. In contrast to SSO, hydrogenated coconut oil (HCO) did not evoke alterations of D-AAOX activity. 5. The activity levels of another peroxisomal enzyme, L-2-hydroxy acid oxidase (L-HAOX), in the liver of rats fed the high-SSO diet vs those fed the control diet were similar. 6. The subcellular distribution of D-AAOX and L-HAOX was not altered in the liver of rats fed the 25% SSO diet during the 10-day period.

Immunochemical relationship of D-amino acid oxidases in various tissues and animals

1. By means of an enzyme immunoassay, the contents of D-amino acid oxidase (DAO) were determined in kidney, liver, cerebellum and lung of hog, but the oxidase was not detectable in heart or cerebrum. 2. The oxidases in kidney, liver and cerebellum of hog were indistinguishable as regards immunoreactivity toward anti-hog kidney DAO antibody, specific activity and molecular weight. 3. The oxidases in rat and dog kidneys immunochemically cross-reacted with anti-hog DAO antibody. 4. The overall structure of the hog oxidase was more similar to that of the dog enzyme than that of the rat, while the structure around the catalytic site of the hog oxidase was more similar to that of the rat oxidase than that of the dog enzyme. 5. On immunoblot analysis, two forms of the oxidase were detected in extracts of hog, rat and dog kidneys.