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Biomedical subjects

R D Walter

Publications and source records attributed to R D Walter.

At least 127 records · Page 7Linked to original sources
PubMed1984

Cyclic AMP-dependent and independent protein kinases in Ascaridia galli.

The occurrence of multiple protein kinases, distinguished with respect to molecular weight and preference for acceptor proteins, was demonstrated in Ascaridia galli. The molecular weights of the cyclic AMP-dependent protein kinase and of phosvitin kinase I and II - both independent of cyclic AMP-were determined to be 160000, greater than 200000 and 40000, respectively. The cyclic AMP-dependent protein kinase preferred histones and kemptide as acceptor substrates; stimulation of enzyme activity was up to 4-fold by cyclic AMP. The activities of phosvitin kinase I and II were found to be effectively inhibited by suramin. The inhibition constants were calculated to be 2 microM and 5 microM, respectively. In addition, stibophen turned out to be a potent inhibitor of phosvitin kinase I; the inhibition constant was determined to be 10 microM.

Animals↗
PubMed1984

Poly(ADP-ribosylation) in Ascaris suum.

Poly(ADP-ribosylation) was demonstrated in the intestinal parasite Ascaris suum, especially in the reproductive tissues. The activity of the ADP-ribosyltransferase was found to depend on divalent cations and to be stimulated by deoxyribonuclease I about 5-fold. The reaction rate was optimal at a temperature of 30 degrees C and at pH about 8.4. The apparent Km value for NAD was estimated to be 0.2mM. The enzyme activity was effectively inhibited by nicotinamide (Ki = 65 microM) benzamide (6 microM), 3-aminobenzamide (10 microM), theophylline (35 microM) and thymidine (50 microM). The type of inhibition by these compounds was found to be competitive with respect to NAD.

Animals↗
PubMed1984

Interaction of amoscanate with the cyclic AMP-phosphodiesterases from Schistosoma mansoni, Onchocerca volvulus and bovine heart.

The anthelmintic compounds amoscanate (4-isothiocyanato-4'-nitrodiphenylamine) and its derivatives CGP 6140 and CGP 8045 are potent inhibitors of the activities of cyclic AMP-phosphodiesterases from schistosomal and filarial worms as well as from both the calmodulin-dependent and the -independent enzyme of bovine heart. As shown for CGP 8045 the type of inhibition is non-competitive with respect to the substrate and the inhibition constants were determined to be in the range of 50 micrograms/ml for the enzymes of parasites and mammalian. It is proposed that the inhibition of cyclic AMP-phosphodiesterase-activity by amoscanate and derivatives - resulting in accumulation of cyclic AMP - might subsequently lead to disturbances in the regulation of metabolic areas like glycogen metabolism which are controlled by cyclic AMP-dependent protein kinases.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1984

Protein kinases in different life stages of Brugia malayi and other filarial worms.

The investigation of protein kinase activity in different life stages of a few filarial worms indicates the presence of different protein kinases and of dissimilarities between the distribution pattern of these enzymes during the development. Phosvitin turned out to be the preferred exogenous acceptor protein, when homogenates of adults of Brugia malayi, Dipetalonema viteae, Setaria cervi and Litomosoides carinii were used as source of enzyme. In contrast to adults the L3-larval and the microfilarial stages demonstrated much lower phosvitin phosphorylating activity and the preference for acidic and basic proteins as phosphate acceptors was about equal. The occurrence of cyclic AMP-dependent protein kinase was established for adults of B. malayi.

Animals↗
PubMed1982

Subcellular distribution of adenylate cyclase, cyclic-AMP phosphodiesterase, protein kinases and phosphoprotein phosphatase in Trypanosoma brucei.

The subcellular distribution of adenylate cyclase, cyclic-AMP phosphodiesterase, protein kinases and phosphoprotein phosphatase in bloodstream forms of Trypanosoma brucei was determined by isopycnic sucrose-gradient centrifugation of post-large-granule extracts. Cyclic-AMP phosphodiesterase was almost entirely soluble whereas adenylate cyclase was membrane-bound. The latter enzyme appeared to be absent from the plasma-membrane fraction but copurified with acid phosphatase and acid phosphodiesterase indicating a possible association with the flagellar pocket. At least two protein kinase activities could be distinguished as based on their distribution profiles in gradients, their preference for exogenously added acceptor protein and their inhibition and stimulation by suramin and nucleoside, respectively. Suramin-sensitive protein kinase co-purified with the plasma-membrane marker alpha-D-glucosidase and a nucleoside-stimulated protein kinase behaved as a typical cell-sap enzyme. Phosphoprotein phosphatase activity was found to be mainly soluble but a small part seemed to be associated with plasma membranes.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1982

Effect of leishmanial excreted factor on the activities of adenylate cyclase from hamster liver and Leishmania tropica.

The carbohydrate segment of the excreted factor of culture cells from L. tropica and L. donovani was shown to interact with the adenylate cyclase from hamster liver. At a concentration of 1 mg/ml the excreted factor inhibited the stimulated activity of the mammalian enzyme by about 50%, independent of the activation by glucagon, 5'-guanylylimidodiphosphate and forskolin, respectively. In contrast to the adenylate cyclase system from hamster liver the enzyme from L. tropica-culture cells was not stimulated by addition of glucagon, 5'-guanylylimidodiphosphate and forskolin. In addition, the activity of the adenylate cyclase from L. tropica was not affected by addition of its endogenous excreted factor.

Adenylyl Cyclase Inhibitors↗
PubMed1981

Inhibition of NADP-linked malic enzyme from Onchocerca volvulus and Dirofilaria immitis by suramin.

NADP-linked malic enzyme (malate dehydrogenase (oxaloacetate-decarboxylating) NADP+, EC 1.1.1.40) has been partially purified from adult Onchocerca volvulus and Dirofilaria immitis. Suramin was found to inhibit the activity of malic enzyme from both filarial worms. The inhibition constants for suramin were calculated to be 0.011 microM and 0.015 microM for the enzymes from O. volvulus and D. immitis, respectively. In the case of NADP-linked malic enzyme from Trypanosoma brucei and chicken liver the inhibition by suramin was less pronounced. The inhibition constants were found to be 0.8 microM and 2.5 microM for the protozoan and vertebrate enzymes, respectively. The type of inhibition was competitive with respect to malate. The Michaelis constants for malate and pyruvate were determined to be 0.9 and 4.5 mM for O. volvulus and 0.85 and 5.0 mM for D. immitis, respectively. The low Km values for malate compared to those for pyruvate and the about 15-fold greater turnover in the direction of decarboxylation compared to carboxylation indicated that malic enzyme from both filarial sources might be involved in an alternative pathway leading from phosphoenolpyruvate via oxaleacetate, malate and pyruvate to lactate. It is suggested, that the inhibition of malic enzyme activity from O. volvulus by suramin might interfere with the generation of NADPH for biosynthetic reactions.

Animals↗
PubMed1980

Effect of suramin on phosphorylation-dephosphorylation reactions in Trypanosoma gambiense.

Suramin which is used as a chemotherapeutic agent against sleeping sickness was tested for its ability to inhibit phosphorylation-dephosphorylation reactions in Trypanosoma gambiense. Protein-kinase I, which is characterized by its preference for acidic acceptor proteins, was found to be strongly inhibited by suramin. The inhibition constant was calculated to be 0.8 microM. The type of inhibition was non-competitive with respect to ATP as well as to substrate protein.

Adenosine Triphosphate↗
PubMed1980

Onchocerca volvulus: effect of suramin on lactate dehydrogenase and malate dehydrogenase.

Lactate dehydrogenase and malate dehydrogenases were partially purified and characterized from adult O. volvulus. The molecular weight of lactate dehydrogenase was determined to be 130 000, those of malate dehydrogenase I and II to be 120 000 and 65 000, respectively. The activities of both malate dehydrogenases and of the lactate dehydrogenase were strongly inhibited by suramin. The inhibition constants were determined to be in the range of 2 microM to 5 microM. The type of inhibition was found to be competitive with respect to the coenzyme NADH and to be non-competitive to the substrates. It is suggested that the mode of action of suramin in the therapy of Onchocerciasis might depend on the blokkade of reoxidation of NADH produced within the glycolytic pathway.

Animals↗
PubMed1979

Evidence for NADH- and NADPH-linked glutamate dehydrogenases in Trypanosoma cruzi epimastigotes.

Two glutamate dehydrogenases, NADH-linked (EC 1.2.1.2) and NADPH-linked (EC 1.2.1.4) were isolated from the epimastigote forms of Trypanosoma cruzi and purified. Both enzymes exist as hexamers. The molecular weights of the native NADH-and NADPH-linked glutamate dehydrogenases were estimated to be 360,000 and 265,000, respectively, and those of the subunits to be 58,000 and 43,000, respectively. The isoelectric point of the NADH-linked dehydrogenase is at pH 5.25 and that of the NADPH-linked enzyme at pH 5.1. The activities of both enzymes are regulated by product inhibition. In addition, purine nucleotides were shown to be potent inhibitors of the NADH-linked glutamate dehydrogenase.

Animals↗
PubMed1979

Inhibition of lactate dehydrogenase activity from Dirofilaria immitis by suramin.

Lactate dehydrogenase from adult D. immitis was partially purified and characterized. The molecular weight of the enzyme was determined to be 130 000. The specific activity of the lactate dehydrogenase was 4.1 U/mg in the direction of NADH-oxidation and 0.38 U/mg protein in the direction of NAD-reduction. The Michaelis constants were determined to be 0.028 mM and 0.9 mM for NADH and NAD, respectively. Suramin was found to be a potent inhibitor of the lactate dehydrogenase activity. The inhibition constant was calculated to be 0.006 mM. The type of inhibition by suramin was competitive with respect to the cofactors. The Km-values for pyruvate and lactate were determined to be 0.3 mM and 11mM, respectively.

Animals↗
PubMed1979

Purification and properties of glucose-6-phosphate dehydrogenase from Leishmania tropical promastigotes.

Glucose-6-phosphate dehydrogenase specific for NADP (EC 1.1.1.49) was purified to homogeneity from Leishmania tropica promastigotes. The enzyme was found to exist as dimer. The molecular weight of the native enzyme was determined to be 110 000, that of the subunit to be 55 000. The occurence of isoenzymes was demonstrated by isoelectrofocusing. Isoelectric points of glucose-6-phosphate dehydrogenase activity were found at pH 5.5 and pH 6.8. The isoenzymes do not differ with respect to Michaelis constants. The Km-values for NADP and glucose-6-phosphate were determined to be 0.012 mM and 0.15 mM respectively. Glucose-6-phosphate dehydrogenase activity was found to be regulated by product inhibition. The inhibition constant for NADPH was calculated to be 0.05 mM.

Animals↗