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Biomedical subjects

R D Walter

Publications and source records attributed to R D Walter.

At least 145 records · Page 8Linked to original sources
PubMed1979

Effect of polyamines on protein kinases activities from Trypanosoma cruzi.

An interaction of polyamines with protein kinases activities from T. cruzi epimastigotes is demonstrated. Spermine and spermidine and less pronounced putrescine are found to inhibit protein kinases activities. In the extract of T. cruzi three protein kinases are distinguished on account of molecular weight (greater than 200 000, 95 000 and 40 000) and preference for acceptor proteins (phosvitin and histones). Especially the activity of the high molecular weight protein kinase which phosphorylates phosvitin is strongly inhibited by spermine and spermidine. The type of inhibition by both polyamines is found to be non-competitive with respect to ATP as well as phosvitin. The inhibition constants for spermine and spermidine are determined to be 1.4 mM and 2.0 nM, respectively.

Animals↗
PubMed1978

Induced amnestic confusional phenomena. Pathology and lateralization.

Additional evidence from pathology findings is presented in support of the proposition that amnestic confusional phenomena, induced by electrical stimulation of the hippocampus in epileptic patients and resembling transient global amnesia, are related to unilateral (dominant hemisphere) cerebral mechanisms.

Amnesia↗
PubMed1978

Multiple protein kinases from Trypanosoma gambiense.

Three protein kinases were distinguished in Trypanosoma gambiense extract. The enzymes preferred phosvitin, histone, and protamine as acceptor proteins, respectively. The amino acid residues of the acceptor proteins which were phosphorylated by these protein-kinase activities were serine and- to less extent- threonine. The protein kinase activities were neither affected by cyclic nucleotides nor by cyclic AMP receptors. The molecular weights of these protein kinases were determined to be greater than 200,000, 95000 and 37000, respectively. The activities of all three protein kinases were affected to varying degrees by nucleotides and nucleosides.

Adenine Nucleotides↗
PubMed1978

Adenosine 3', 5'-cyclic monophosphate-binding proteins from Trypanosoma gambiense.

Two cyclic AMP-binding proteins, not identical with regulatory subunits of protein kinases, have been isolated from Trypanosoma gambiense. The cyclic AMP receptors were separated by gel chromatography on the basis of their molecular weights. The binding constants of the high and the low molecular weight receptors for cyclic AMP were determined to be 0.4 muM and 0.6 muM, respectively. Cyclic IMP and cyclic GMP compete with cyclic AMP for the binding sites of both receptors. The cyclic AMP binding of the low molecular weight receptor was competitively inhibitied by adenine derivatives. The binding capacity of the high molecular weight receptor was enhanced about two-fold by proteolytic modification with trypsin.

Adenosine↗
PubMed1978

Effect of cyclic AMP on transformation and proliferation of leishmania cells.

A correlation between cyclic AMP (adenosine 3' : 5'-monophosphate) concentration within Leishmania cells and proliferation and transformation is demonstrated. By addition of dibutyryl cyclic AMP and cyclic AMP-phosphodiesterase inhibitors to the culture medium the intracellular level of cyclic AMP was increased. In the presence of 1mM caffeine the level of cyclic AMP accumulated in L. tropica promastigotes from 90 pmoles up to 380 pmoles per 10(9) cells, whereas the proliferation rate decreased to 50%. In the case of L. donovani the transformation of amastigotes to promastigotes was inhibited by addition of dibutyryl cyclic AMP as well as caffeine and papaverine. Especially caffeine (2mM) and papaverine (0.1mM) reduced the transformation rate to less than 5% after 48 h, compared to 35% of the control.

Bucladesine↗
PubMed1977

Evoked response and after-discharge thresholds to electrical stimulation in temporal lobe epileptics.

The records of electrical stimulation of 30 psychomotor epileptics were examined for threshold levels of evoked responses and after-discharge production. Comparisons were made between anatomical sites, operated and nonoperated structures, and different disease states. It was found that patients with hippocampal sclerosis (HS) had higher thresholds in structures on the operated side. The patients with lesions other than HS were found to differ from those with hippocampal sclerosis in that there were no differences found between their diseased and nondiseased structures. For both patient groups, the amygdala had a much higher threshold for after-discharge production than either the hippocampus or the hippocampal gyrus.

Adolescent↗
PubMed1977

Inhibition of protein kinase activity from Trypanosoma cruzi and Trypanosoma gambiense by 3'-deoxyadenosine.

3'-Deoxydadenosine was found to be a potent inhibitor of nucleoside-stimulated protein kinase activity from culture forms of Trypanosoma cruzi and bloodstream forms of Trypanosoma gambiense. The type of inhibition by 3'-deoxyadenosine was competitive with respect to ATP. The inhibition constants for 3'-deoxyadenosine were determined to be 0.11mM and 0.085mM for the enzyme from T. cruzi and T. gambiense, respectively. The apparent Km value for ATP was 0.2mM for both enzymes. 2'-Deoxyadenosine was less effective as inhibitor of the protein kinase activity. The inhibition constants were calculated to be 0.8mM and 0.67mM, respectively.

Adenosine Triphosphate↗
PubMed1976

Nucleoside-dependent protein kinase from Trypanosoma gambiense.

A nucleoside-dependent protein kinase (EC 2.7.1.37) was partially purified from Trypanosoma gambiense, the pathogenic agent of sleeping sickness. This enzyme catalyzes the phosphorylation of histone and protamine. Various nucleosides at the concentration of 10(-4) M stimulated the histone kinase activity about two-fold, whereas cyclic AMP and cyclic GMP were without effect. The pH-optimum for histone phosphorylation was at about pH 7.0. The enzyme activity absolutely depends on Mg2+, Mn2+ or Co2+. The apparent Km-value for histone was 0.3 mg/ml and those for ATP were 2 - 10(-4) M and 6 - 10(-5) M in the absence or presence of 10(-4) M adenosine respectively. IDP and ADP complete with ATP. The inhibition constants were calculated to be 2 - 10(-4) M and 2.5 - 10(-4) M, respectively. The molecular weight of the histone kinase was found to be 95 000 by gel filtration and 88 000 by sedimentation in a sucrose gradient.

Animals↗
PubMed1976

A comparison of EEG seizure patterns recorded with surface and depth electrodes in patients with temporal lobe epilepsy.

Surface and depth EEG seizure patterns were compared in 34 patients with intractable temporal lobe epilepsy in whom depth EEG electrodes had been chronically implanted in order to localize epileptogenic sites with a view to surgery. EEG records accompanied by clinical seizures, auras, no behavioral changes, as well as records for which no behavioral observations had been made, were judged with respect to the manner in which seizure activity originating unilaterally in the depth of one of the temporal lobes spread to the surface. For each EEG record, the onset of seizure activity in depth was classified as being focal or regional in form, and seizure activity was judged as: (1) not spreading to the surface, (2) spreading bilaterally and synchronously to the surface, (3) spreading initially to the surface ipsilateral to the depth site(s) in which the electrographic seizure first appeared, or (4) spreading initially to the surface contralateral to the depth site(s) in which the seizure activity initially occurred. EEG seizure activity was found to be less likely to propagate to the surface for those records that were either unaccompanied by behavior changes or accompanied only by auras than for those records accompanied by clinical seizures. In records accompanied by clinical seizures, seizure activity commonly propagated to the surface in a bilateral and synchronous fashion and was also found to spread initially to the ipsilateral but not to the contralateral surface. Anatomical and electrophysiological data accounting for the occurrence of ipsilateral spread were discussed. Diagnostic usefulness of surface recordings during clinical seizures in temporal lobe epilepsy was discussed.

Animals↗
PubMed1976

Properties of 3',5'-cyclic-AMP phosphodiesterase from Paragonimus africanus metacercariae.

3',5'-Cyclic-AMP 5'-nucleotidohydrolase (cAMP phosphodiesterase, EC 3.1.4.17) was partial purified from metacercariae of Paragonimus africanus. The enzyme activity absolutely depends on Mg2 or Mn2+. The pH-optimum of the cAMP phosphidiesterase was found at pH 8.0. The Michaelis constant for cAMP was determined to be 5 X 10(-6) M. Papaverine deoxyadenosine, theophylline and adenosine were found to be competitive inhibitors of the enzyme activity. The inhibitor constants were calculated to be 13 X 10(-6)M, 25 X 10(-5)M, and 35 X 10(-5)M, and 85 X 10(-5)M,respectively. The molecular weight of the cAMP phosphodiesterase was estimated to be about 40 000 by gel filtration.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1975

A purine nucleoside hydrolase from Trypanosoma gambiense, purification and properties.

A purine nucleoside hydrolase from Trypanosoma gambiense was purified 160-fold. Preferred substrates of the reaction were adenosine, inosine and guanosine with a maximum of activity at pH 5.4. Competitive inhibitors of the adenosine hydrolysis were dimethylallyl adenosine, 6-methylmercaptopurine riboside, tubercidin, formycin B, 6-mercaptopurine riboside and deoxyadenosine. A metabolic scheme of adenosine nomophosphate salvage synthesis is discussed.

Adenine Phosphoribosyltransferase↗