Search PubMed⌕ Search

Biomedical subjects

R D Walter

Publications and source records attributed to R D Walter.

At least 109 records · Page 6Linked to original sources
PubMed1988

Plasmodium falciparum: association with erythrocytic superoxide dismutase.

Levels of superoxide dismutase (SOD) activity and its properties in Plasmodium falciparum-infected erythrocytes, isolated parasites, and noninfected erythrocytes were studied. A higher specific activity was found in P. falciparum-infected erythrocytes compared to noninfected erythrocytes, resulting from the lower protein content of infected cells and not enzyme synthesis by the parasite, as the superoxide dismutase activity expressed per number of cells was decreased. Superoxide dismutase from noninfected erythrocytes and isolated P. falciparum parasites showed similar sensitivities to various inhibitors and had identical molecular weights and electrophoretic mobilities. These results support the hypothesis of uptake and use of the erythrocytic SOD enzyme by the parasite as a possible mechanism of defense against oxidative stress.

Animals↗
PubMed1988

Preparation and shipping of Onchocerca volvulus material.

Instructions are provided for selection of nodules, isolation of female Onchocerca volvulus and shipping to obtain suitable, intact and live worms for drug-screening and metabolic studies in vitro as well as material for isolation of enzymes, receptors, antigens etc.

Animals↗
PubMed1988

In vitro maintenance of Onchocerca volvulus for harvest of excretory and secretory products.

Recommendations are given for maintenance of female Onchocerca volvulus; conditions as standardized here for drug screening and harvest of secreted-excreted products resulted in survival of worms in culture medium for up to four and six weeks in absence and presence of serum, respectively. As parameter for viability of worms lactate excretion was determined beside control of motility.

Animals↗
PubMed1987

Plasmodium falciparum: S-adenosyl-L-methionine decarboxylase.

Putrescine-dependent S-adenosyl-L-methionine decarboxylase has been detected in the malaria parasite Plasmodium falciparum. Mg2+ did not affect the enzyme activity. The apparent Km value of the plasmodial enzyme for adenosyl-methionine was found to be 33 microM. Methylglyoxal bis(guanylhydrazone) competitively inhibited the enzyme activity with respect to adenosylmethionine. The inhibition constant for methylglyoxal bis(guanylhydrazone) was determined to be 0.46 microM. Spermidine was the main polyamine detected in the parasite. There was significant decrease in the S-adenosyl-L-methionine decarboxylase activity when the infected erythrocytes were incubated with chloroquine and mefloquine for 2 hr at 1 and 10 microM, respectively. Since at similar concentrations these drugs did not directly affect the plasmodial enzyme activity, the interaction of these drugs with the polyamine biosynthesis remains unclear.

Adenosylmethionine Decarboxylase↗
PubMed1987

Putrescine-activated S-adenosylmethionine decarboxylase from Acanthamoeba culbertsoni.

Acanthamoeba culbertsoni, the free living pathogenic amoeba responsible for fatal meningoencephalitis, contains an S-adenosylmethionine decarboxylase (EC 4.1.1.50) which is strongly activated by putrescine and to a lesser extent by cadaverine; spermidine, spermine, diaminopropane and 1,6-diaminohexane are inactive. Methylglyoxal bis-(guanylhydrazone) competitively inhibited the enzyme with a Ki value of 123 microM. The enzyme was strongly inhibited by berenil (Ki = 0.5 microM) and to a lesser extent by pentamidine. The putrescine-activated enzyme is inhibited by MgCl2. The apparent molecular weight of 110,000 and its enzymatic properties indicate that the enzyme has characteristics intermediate between the bacterial and eukaryotic S-adenosylmethionine decarboxylases.

Adenosylmethionine Decarboxylase↗
PubMed1987

Polyamine metabolism in filarial worms.

The human and animal filarial parasites Onchocerca volvulus, Dirofilaria immitis, Brugia patei and Litomosoides carinii contained low levels of putrescine but much higher levels of spermidine and spermine as estimated by ion-pair high pressure liquid chromatography; N-acetylated polyamines were present only in minute amounts. Enzyme activities of ornithine decarboxylase (EC 4.1.1.17) and arginine decarboxylase (EC 4.1.1.19), respectively, were not detectable. Experiments carried out with O. volvulus and D. immitis demonstrated the uptake and bioconversion of labeled polyamines. There is evidence for the existence of a complete reverse pathway generating putrescine from spermidine and spermine, respectively, in both worms. N-Acetylating enzyme activities were detected in 100,000 X g preparations of homogenates from D. immitis which were capable to acetylate putrescine, spermidine and spermine. Long term incubation of the worms in the presence of labeled polyamines resulted in the excretion of putrescine and N-acetylputrescine.

Animals↗
PubMed1987

Filaricidal effect of mefloquine on adults and microfilariae of Brugia patei and Brugia malayi.

Mefloquine, DL-erythro-2,8-bis(trifluoromethyl)-alpha-(2-piperidyl)-4-quinoline methanolhydrochloride, a recently developed antimalarial drug shows filaricidal activity against larval and adult stages of Brugia patei and B. malayi maintained "in vitro". In the concentration range of 10 to 2 microM mefloquine paralysed and killed the filarial worms within 10 h and 3 d, respectively. The lethal effect of mefloquine treatment on larval and adult worms was shown by loss of motility as well as by decrease of lactate excretion by adults. Chloroquine at a concentration of 10 microM did not affect motility and survival of microfilariae and adults of B. patei. Addition of serum to the cultivation medium abolished the filaricidal effect, possibly due to the tight binding of mefloquine to serum proteins, thereby affecting the uptake of the drug into the parasite.

Animals↗
PubMed1986

Plasmodium falciparum: inhibition of dolichol kinase by mefloquine.

Dolichol kinase, a rate limiting enzyme for the supply with dolichyl monophosphate as glycosyl carrier lipid, was demonstrated in Plasmodium falciparum. The enzyme was found to be associated with the pellet fraction and to depend on cytidine triphosphate as phosphoryl donor. The apparent Km values of the plasmodial enzyme were determined to be 0.8 mM for cytidine triphosphate and 17 micrograms ml-1 for dolichol. In the presence of 0.5 mM mefloquine, the inhibition of enzyme activity was found to be about 50%.

Animals↗
PubMed1986

Altered dihydrofolate reductase in pyrimethamine-resistant Plasmodium falciparum.

Dihydrofolate reductase (EC 1.5.1.3, tetrahydrofolate dehydrogenase), the target enzyme for the chemotherapeutic attack by pyrimethamine, has been studied in drug-sensitive and resistant strains of Plasmodium falciparum. No evidence was found for overproduction of this enzyme in drug-resistant strains. Results presented here indicate that pyrimethamine resistance of P. falciparum depends on a modified dihydrofolate reductase, which shows less affinity for pyrimethamine and dihydrofolate. The inhibition constants for pyrimethamine increased from 0.19 nM for the drug-sensitive strain FCH-5 to 4.1 and 21.6 nM for the drug-resistant strains FVOR and K 1, respectively. In addition, the Km-values for dihydrofolate increased from 2.5 microM to 21 and 28 microM, respectively. The type of inhibition by pyrimethamine changed from competitive with respect to dihydrofolate in drug-sensitive strain to non-competitive in drug-resistant strains of P. falciparum.

Animals↗
PubMed1986

Phosphoenolpyruvate carboxykinase from Onchocerca volvulus and O. gibsoni.

Phosphoenolpyruvate carboxykinase, a rate-limiting enzyme at the branchpoint of phosphoenolpyruvate (PEP), was demonstrated in Onchocerca volvulus and O. gibsoni. The activity of PEP-carboxykinase from both filarial worms depends absolutely on the presence of divalent cations; in addition to Mg2+ the enzyme activity was strongly activated by Mn2+. The Michaelis constants for PEP, GDP and KHCO3 of the PEP-carboxykinase from O. volvulus were determined to be 0.16 mM, 0.15 mM and 20 mM, respectively; those of the enzyme from O. gibsoni were 0.16 mM, 0.13 mM and 12 mM. Quinolinate was found to be a potent inhibitor of the enzyme from both filarial worms. The inhibition constants were determined to be 11 microM and 15 microM for the enzyme from O. volvulus and O. gibsoni. It is suggested that the activity of PEP-carboxykinase, the initial enzyme of the alternate route from PEP to succinate, may be regulated by ATP-levels. The inhibition constants for ATP were determined to be 0.26 mM and 0.13 mM for the enzyme from O. volvulus and O. gibsoni.

Adenosine Triphosphate↗
PubMed1985

Nippostrongylus brasiliensis: occurrence of multiple protein kinases.

The presence of cyclic AMP-dependent protein kinase and phosvitin kinases, with activity independent of cyclic nucleotides, was shown in the intestinal nematode Nippostrongylus brasiliensis. The activity of the cyclic AMP-dependent protein kinase was found to be enhanced about 8-fold in the presence of 10(-7) M cyclic AMP; the apparent Km values were determined to be 20 microM and 80 microM for ATP and kemptide, respectively. The molecular weight of the holoenzyme was about 170 000. Two phosvitin kinases could be isolated and distinguished by their molecular weights of 600 000 and 40 000. The activity of the high-molecular-weight phosvitin kinase was effectively inhibited by suramin and heparin. The apparent Km values were found to be 30 microM and 0.1 mg/ml for ATP and phosvitin, respectively. In the case of the low-molecular-weight phosvitin kinase the apparent Km values for ATP and phosvitin were found to be 30 microM and 0.6 mg/ml, respectively. The investigation of different developmental stages of N. brasiliensis revealed a marked higher level of protein kinase activity in the L4 larvae compared to L3 larvae and adults.

Animals↗
PubMed1985

Dolichol kinase in Ascaris suum and Onchocerca volvulus.

Dolichol kinase was demonstrated in the microsomal fraction of Ascaris suum and Onchocerca volvulus. The enzyme from nematodes exhibited specificity for CTP as phosphoryl donor and was found to be inhibited by the reaction product CDP. Enzyme activity was optimal at pH 7.4, in the temperature range between 30 degrees and 37 degrees C, and in the presence of 0.5% Triton X-100. In addition, the enzyme was found to depend on divalent cations for activity; Mg2+ being more effective than Mn2+ and Ca2+. The dolichol kinase from both nematodes was shown to be independent of Ca2+-calmodulin for activity. The apparent Km values for dolichol were determined to be 7.5 and 9.0 micrograms ml-1 for the enzyme from A. suum and O. volvulus, respectively. Those for CTP were estimated to be 0.85 and 0.75 mM, respectively.

Animals↗
PubMed1985

Parasite-specific inhibition of 5'-nucleotidase from Onchocerca volvulus and Dirofilaria immitis by the amoscanate-derivative CGP 8065.

The presence of 5'-nucleotidase was demonstrated in Onchocerca volvulus and Dirofilaria immitis; the bulk of activity was found in the particulate fraction. The enzyme of filarial worms exhibited a broad pH-optimum between 6.4 and 8.0 and substrate specificity for nucleotides compared to glucose-6-phosphate and p-nitrophenyl phosphate. The apparent Km-values for AMP were found to be 0.15 mM and 0.22 mM for the enzyme from O. volvulus and D. immitis, respectively. The activity of 5'-nucleotidase from both filarial worms was effectively inhibited by the filaricidal compound CGP 8065, a dithiocarbamate-derivative of amoscanate, whereas the 5'-nucleotidase from rat liver was not affected. The parasite-specific inhibition by CGP 8065 was found to be reversible and to be competitive with respect to the substrate AMP. The inhibition constants were calculated to be 24 microM and 8 microM for the enzyme from O. volvulus and D. immitis, respectively.

5'-Nucleotidase↗
PubMed1985

Effect of amoscanate derivative CGP 8065 on aminoacyl-tRNA synthetases in Ascaris suum.

Evidence is provided for the occurrence of a multienzyme complex consisting of several aminoacyl-tRNA synthetases besides 'free enzymes' in Ascaris suum. The molecular mass of this complex was calculated to be about 10(6) daltons, compared to about 150 000 daltons for the seryl-tRNA synthetase. Leucyl-, isoleucyl-, arginyl- and lysyl-tRNA synthestases were found in the high molecular weight fraction. The Michaelis constants of these aminoacyl-tRNA synthetases were found to be in the range of 4 to 10 microM for amino acids and of 0.1 to 1.0 mM for ATP. Leucyl- and isoleucyl-tRNA synthetase interact with the amoscanate-derivative CGP 8065. The inhibition constants were determined to be 34 microM and 8 microM, respectively. The type of inhibition was found to be competitive with respect to ATP. It is proposed that the interference of CGP 8065 with the charging of tRNA might be another target for the chemotherapeutic attack of this amoscanate derivative.

Amino Acyl-tRNA Synthetases↗
PubMed1985

Anger biting. The hidden impulse.

Based upon the paralogical reasoning of the anger-impulsive biter, this paper addresses the overload of emotional catharsis which can block a full memory of the biting event and suspend the logical infrastructure of rational behavior. In an effort to overcome these types of investigative difficulties, the paper suggests an approach to resolve dilemma through decompressing the emotional content into path ways of logical understanding. By offering a network of rationale hooks, the perpetrator becomes better equipped to acknowledge the deed.

Anger↗
PubMed1985

Parasite-specific interaction of N-[4-(4'nitroanilino)-phenyl]-S-(beta-carboxyethyl)-dithiocar bamic acid-ester with arginyl-tRNA-synthetase from Dirofilaria immitis.

A potent inhibition of arginyl-tRNA-synthetase from Dirofilaria immitis by N-[4-(4'nitroanilino)-phenyl]-S-(beta-carboxylethyl)-dith iocarbamic acid-ester (CGP 8065) is demonstrated, which indicates the charging of amino acids to tRNA as a possible target for the chemotherapeutic attack by this filaricidal compound. CGP 8065 competes with ATP; the inhibition constant was determined to be 13 micrograms ml-1 (34 microM). The Michaelis constants for arginine and ATP were found to be 5 microM and 0.4 mM, respectively. The inhibition of arginyl-tRNA-synthetase by CGP 8065 was shown to be specific for D. immitis; the isofunctional enzymes from Ascaris suum and rat liver were not affected.

Amino Acyl-tRNA Synthetases↗