Superoxide regulation of endothelin-converting enzyme

Reactive oxygen species (ROS) act as signaling molecules in the cardiovascular system, regulating cellular proliferation and migration. However, an excess of ROS can damage cells and alter endothelial cell function. We hypothesized that endogenous mechanisms protect the vasculature from excess levels of ROS. We now show that superoxide can inhibit endothelin-converting enzyme activity (ECE) and decrease endothelin-1 synthesis. Superoxide inhibits ECE but hydrogen peroxide and nitric oxide do not. Superoxide inhibits ECE by ejecting zinc from the enzyme, and the addition of exogenous zinc restores enzymatic activity. Superoxide may inhibit other zinc metalloproteinases by a similar mechanism and may thus play an important role in regulating the biology of blood vessels.     

Oxidative phosphorylation supported by an alternative respiratory pathway in mitochondria from Euglena

The effect of antimycin, myxothiazol, 2-heptyl-4-hydroxyquinoline-N-oxide, stigmatellin and cyanide on respiration, ATP synthesis, cytochrome c reductase, and membrane potential in mitochondria isolated from dark-grown Euglena cells was determined. With L-lactate as substrate, ATP synthesis was partially inhibited by antimycin, but the other four inhibitors completely abolished the process. Cyanide also inhibited the antimycin-resistant ATP synthesis. Membrane potential was collapsed (<60 mV) by cyanide and stigmatellin. However, in the presence of antimycin, a H(+)60 mV) that sufficed to drive ATP synthesis remained. Cytochrome c reductase, with L-lactate as donor, was diminished by antimycin and myxothiazol. Cytochrome bc(1) complex activity was fully inhibited by antimycin, but it was resistant to myxothiazol. Stigmatellin inhibited both L-lactate-dependent cytochrome c reductase and cytochrome bc(1) complex activities. Respiration was partially inhibited by the five inhibitors. The cyanide-resistant respiration was strongly inhibited by diphenylamine, n-propyl-gallate, salicylhydroxamic acid and disulfiram. Based on these results, a model of the respiratory chain of Euglena mitochondria is proposed, in which a quinol-cytochrome c oxidoreductase resistant to antimycin, and a quinol oxidase resistant to antimycin and cyanide are included.     

Reactivity of horseradish peroxidase compound II toward substrates: kinetic evidence for a two-step mechanism

Transient kinetic analysis of biphasic, single turnover data for the reaction of 2,2'-azino-bis[3-ethylbenzthiazoline-6-sulfonic acid] (ABTS) with horseradish peroxidase (HRPC) compound II demonstrated preequilibrium binding of ABTS (k(+5) = 7.82 x 10(4) M(-)(1) s(-)(1)) prior to rate-limiting electron transfer (k(+6) = 42.1 s(-)(1)). These data were obtained using a stopped-flow method, which included ascorbate in the reaction medium to maintain a low steady-state concentration of ABTS (pseudo-first-order conditions) and to minimize absorbance changes in the Soret region due to the accumulation of ABTS cation radicals. A steady-state kinetic analysis of the reaction confirmed that the reduction of HRPC compound II by this substrate is rate-limiting in the complete peroxidase cycle. The reaction of HRPC with o-diphenols has been investigated using a chronometric method that also included ascorbate in the assay medium to minimize the effects of nonenzymic reactions involving phenol-derived radical products. This enabled the initial rates of o-diphenol oxidation at different hydrogen peroxide and o-diphenol concentrations to be determined from the lag period induced by the presence of ascorbate. The kinetic analysis resolved the reaction of HRPC compound II with o-diphenols into two steps, initial formation of an enzyme-substrate complex followed by electron transfer from the substrate to the heme. With o-diphenols that are rapidly oxidized, the heterolytic cleavage of the O-O bond of the heme-bound hydrogen peroxide (k(+2) = 2.17 x 10(3) s(-)(1)) is rate-limiting. The size and hydrophobicity of the o-diphenol substrates are correlated with their rate of binding to HRPC, while the electron density at the C-4 hydroxyl group predominantly influences the rate of electron transfer to the heme.     

Stopped-flow and steady-state study of the diphenolase activity of mushroom tyrosinase

The reaction of mushroom (Agaricus bisporus) tyrosinase with dioxygen in the presence of several o-diphenolic substrates has been studied by steady-state and transient-phase kinetics in order to elucidate the rate-limiting step and to provide new insights into the mechanism of oxidation of these substrates. A kinetic analysis has allowed for the first time the determination of individual rate constants for several of the partial reactions that comprise the catalytic cycle. Mushroom tyrosinase rapidly reacts with dioxygen with a second-order rate constant k(+8) = 2.3 x 10(7) M(-)(1) s(-)(1), which is similar to that reported for hemocyanins [(1.3 x 10(6))-(5.7 x 10(7)) M(-)(1) s(-)(1)]. Deoxytyrosinase binds dioxygen reversibly at the binuclear Cu(I) site with a dissociation constant K(D)(O)()2 = 46.6 microM, which is similar to the value (K(D)(O)()2 = 90 microM) reported for the binding of dioxygen to Octopus vulgaris deoxyhemocyanin [Salvato et al. (1998) Biochemistry 37, 14065-14077]. Transient and steady-state kinetics showed that o-diphenols such as 4-tert-butylcatechol react significantly faster with mettyrosinase (k(+2) = 9.02 x 10(6) M(-)(1) s(-)(1)) than with oxytyrosinase (k(+6) = 5.4 x 10(5) M(-)(1) s(-)(1)). This difference is interpreted in terms of differential steric and polar effects that modulate the access of o-diphenols to the active site for these two forms of the enzyme. The values of k(cat) for several o-diphenols are also consistent with steric and polar factors controlling the mobility, orientation, and thence the reactivity of substrates at the active site of tyrosinase.     

Localization of a 24-kDa collagenase in the Gymnorhynchus gigas plerocercoid

A 24-kDa collagenase was localized in the Gymnorhynchus gigas plerocercoid immunohistochemically by peroxidase complex staining using polyclonal antibodies from NMRI mouse sera immunized with purified enzyme. Immunoreactivity was determined at different parts of the body (scolex, vesicle and caudal region) and mainly localized in microtriches and parenchymal tissues of the scolex and vesicle. These results, along with the absence of the enzyme in the plerocercoid excretion-secretion products, suggest that the 24-kDa collagenase is produced by parenchymal cells in the anterior region and transported to the outer regions of the worm It is possible that the enzyme plays an important role in degrading parasite tissues during the moulting process.     

Sequence and diversity of MHC <Emphasis Type="Italic">DQA</Emphasis> and<Emphasis Type="Italic"> DQB</Emphasis> genes of the owl monkey<Emphasis Type="Italic"> Aotus nancymaae</Emphasis>

The New World primate Aotus nancymaae has been recommended by the World Health Organization (WHO) as a model for evaluation of malaria vaccine candidates, given its susceptibility to experimental infection with the human malaria parasites Plasmodium falciparum and Plasmodium vivax. We present here the nucleotide sequences of the complete cDNA of MHC-DQA1 and of the polymorphic exon 2 segments of MHC-DQB1/DQB2. In a group of three nonrelated animals captured in the wild, five alleles of MHC-DQA1 could be identified. They all belong to one lineage, namely Aona-DQA1*27. This lineage has not been described in any other New World monkey species studied. In a group of 19 unrelated animals, 14 Aona-DQB1 alleles could be identified which are grouped into the two lineages Aona-DQB1*22 and Aona-DQB1*23. These lineages have been described previously in the common marmoset and cotton-top tamarin. In addition, two Aona-DQB2 sequences could be identified which are highly similar to HLA-DQB2 sequences. Essential amino acid residues contributing to MHC DQ peptide binding pockets number 1 and 4 are conserved or semi-conserved between HLA-DQ and Aona-DQ molecules, indicating a capacity to bind similar peptide repertoires. These results fully support the use of Aotus monkeys as an animal model for evaluation of future subunit vaccine candidates.     

Sequence and diversity of DRB genes of Aotus nancymaae, a primate model for human malaria parasites

 The New World primate Aotus nancymaae is susceptible to infection with the human malaria parasite Plasmodium falciparum and Plasmodium vivax and has therefore been recommended by the World Health Organization as a model for evaluation of malaria vaccine candidates. We present here a first step in the molecular characterization of the major histocompatibility complex (MHC) class II DRB genes of Aotus nancymaae (owl monkey or night monkey) by nucleotide sequence analysis of the polymorphic exon 2 segments. In a group of 15 nonrelated animals captivated in the wild, 34 MHC DRB alleles could be identified. Six allelic lineages were detected, two of them having human counterparts, while two other lineages have not been described in any other New World monkey species studied. As in the common marmoset, the diversity of DRB alleles appears to have arisen largely by point mutations in the β-pleated sheets and by frequent exchange of fixed sequence motifs in the α-helical portion. Pairs of alleles differing only at amino acid position b86 by an exchange of valine to glycine are present in Aotus, as in humans. Essential amino acid residues contributing to MHC DR peptide binding pockets number 1 and 4 are conserved or semiconserved between HLA-DR and Aona-DRB molecules, indicating a capacity to bind similar peptide repertoires. These results support fully our using Aotus monkeys as an animal model for evaluation of future subunit vaccine candidates. Received: 10 August 1999 / Revised: 11 October 1999     

B-Type and C-Type Natriuretic Peptides Modify Norepinephrine Uptake in Discrete Encephalic Nuclei of the Rat

SUMMARY 1. We previously demonstrated that atrial natriuretic factor and B- and C-type natriuretic peptides (ANF, BNP, and CNP, respectively) modified catecholamine metabolism by increasing the neuronal uptake and decreasing the neuronal release of norepinephrine in the rat hypothalamus. The aim of the present work was to study the effects of natriuretic peptides BNP and CNP on norepinephrine uptake as an index of the amine metabolism in discrete areas and nuclei of the central nervous system (CNS) of the rat.2. Experiments were carried out in vitro using the punchout technique in diverse areas and nuclei of rat CNS. Results showed that 100 nM BNP and 1 nM CNP increased norepinephrine (NE) uptake in all brain areas and nuclei studied.3. Present results permit us to conclude that BNP and CNP regulate NE metabolism independently of the encephalic area or nucleus involved. In fact, NE uptake increased in nuclei related to the regullation of cardivascular activity as well as nuclei associated with endocrine metabolism and hydrosaline homeostasis. These observations suggest that BNP and CNP may be involved in the regulation of these physiological processes in an indirect manner through modifications of noradrenergic neurotransmission. Present findings provide futher support to the hypothesis that CNP would be the main natriuretic peptide in brain. Furthermore, previous as well as present results support the role of the natriureic peptides as neuromodulators of noradrenergic transmission at the presynaptic level.     

Dietary alterations in protein,carbohydrates and fat increase liver protein-turnover rate and decrease overall growth rate in the rainbow trout (Oncorhynchus mykiss

We have determined the protein-turnover rates and nucleic-acid concentrations in the liver of trout (Oncorhynchus mykiss) fed on two different isocaloric diets: low-protein/high-fat and non-carbohydrate/high-fat. Compared to controls, the partial replacement of protein with fat significantly decreased the protein accumulation rate and protein-retention efficiency in the liver whilst increasing the fractional protein-synthesis and protein-degradation rates as well as protein-synthesis efficiency. The complete replacement of carbohydrates with fat significantly lowered the protein-accumulation rate and protein-retention efficiency, but enhanced both the protein-synthesis and protein-degradation rates as well as protein-synthesis capacity. The protein:DNA and RNA:DNA ratios decreased considerably on both diets. Total DNA decreased in fish on a low-protein/high-fat diet but did not change in those on a non-carbohydrate/high-fat diet. The absolute protein-synthesis rate registered no significant change under any of the nutritional conditions. Both the experimental diets did however raise the fractional protein-synthesis rate significantly, due to enhanced protein-synthesis efficiency when protein was partially replaced with fat and to enhanced protein-synthesis capacity when carbohydrates were completely replaced with fat. Our results show the capacity of the liver to adapt its turnover rates and conform to different nutritional conditions. They also point to the possibility of controlling fish growth by dietary means.     

Kinetic study of the oxidation of 3-hydroxyanisole catalysed by tyrosinase

Tyrosinase hydroxylates 3-hydroxyanisole in the 4-position. The reaction product accumulates in the reaction medium with a lag time (tau) which diminishes with increasing concentrations of enzyme and lengthens with increasing concentrations of substrate, thus fulfilling all the predictions of the mechanism proposed by us for 4-hydroxyphenols. The kinetic constants obtained, kcatM = (46.87 +/- 2.06) s-1 and KmM = (5.40 +/- 0.60) mM, are different from those obtained with 4-hydroxyanisole, kcatM = (184.20 +/- 6.1) s-1 and KmM = (0.08 +/- 0.004) mM. The catalytic efficiency, kcatM/KmM is, therefore, 265.3 times greater with 4-hydroxyanisole. The possible rate-determining steps for the reaction mechanism of tyrosinase on 3- and 4-hydroxyanisole, based on the NMR spectra of both monophenols, are discussed. These possible rate-determining steps are the nucleophilic attack of hydroxyl's oxygen on the copper and the electrophilic attack of the peroxide on the aromatic ring. Both steps may be of similar magnitude, i.e. take place in the same time scale.