Biomedical subjects

D Palm

Publications and source records attributed to D Palm.

At least 37 records · Page 2Linked to original sources

PubMed1995

Dose-effect and kinetic-dynamic relationships of the beta-adrenoceptor blocking properties of various doses of talinolol in healthy humans.

Twelve healthy subjects were investigated on six separate occasions at least 1 week apart when they either received a single oral dose of 80 mg propranolol; 25, 50, 100, or 400 mg talinolol; or placebo (double-blinded, period-balanced six-way cross-over design). The subjects were investigated during supine rest and performed supine bicycle ergometry 0200, 0500, 0730, 1000, and 2400 h after dosing. Isoprenaline (ISO) and epinephrine (EPI) were infused intravenously (i.v.) at a constant infusion rate of 1 microgram/min for 10 min, at 0315 and 0400 h after dosing, respectively. At various timepoints, blood was drawn for the high-performance liquid chromatography (HPLC) determination of the plasma concentrations of talinolol's enantiomers and for the ex vivo in vitro determination of beta 1- and beta 2-adrenoceptor binding and related concentrations by radioreceptor assay (RRA). Talinolol was confirmed to bind to beta-adrenoceptors with moderate affinity but to act as a highly selective and efficient beta 1-adrenoceptor antagonist in terms of the relative degree and duration of its ergometric effects. At doses < or = 100 mg talinolol hardly altered the reduction of estimated vascular total peripheral resistance (TPR) in response to the intravenous infusion of ISO and EPI. Only at doses of 400 mg did talinolol more closely approximate the effects of propranolol, which lead to a loss of the vasodilatory actions of EPI ("EPI reversal"). On the average, there was a smoothly linear relationship between the ergometric treatment effects and log-transformed dose, the logtransformed concentrations of the S(-)-enantiomer measured by HPLC, and the RRA-derived estimated occupancies beta 1-adrenoceptors.

Adrenergic beta-Antagonists↗

PubMed1995

Choroid plexus electrolytes and ultrastructure following transient forebrain ischemia.

A temporal profile of lateral and fourth ventricle rat choroid plexus (LVCP and 4VCP, respectively) tissue injury and recovery was determined using alterations in K, Na, and H2O content and ultrastructure after 10 min of transient forebrain ischemia (TFI). At 0.5 h postischemia the LVCP displayed a maximum reduction in K content by 32% and a significant increase in Na content by 85% and H2O content by 22%. LVCP tissue K, Na, and H2O content returned to sham values by 24 h postischemia. Ultrastructural changes appeared more severe between 0.5 and 12 h postischemia, whereas by 24 h, normal ultrastructure was restored. Elevations in 4VCP tissue Na (P < 0.05) and H2O content, which were less than those in LVCP, gradually reached a maximum by 24 h compared with sham. No change in 4VCP tissue ultrastructure was observed. These results indicate that the LVCP tissue is more vulnerable than 4VCP in the bilateral carotid artery occlusion model but that it recovers in a timely manner after TFI. Furthermore, the ability of the LVCP tissue to rapidly recover suggests its functional importance in helping to restore brain homeostasis.

Animals↗

PubMed1995

N-acetylcysteine enhances hippocampal neuronal survival after transient forebrain ischemia in rats.

BACKGROUND AND PURPOSE: Free radical scavengers enhance neuronal survival in some models of transient forebrain ischemia. Recent experiments have suggested that N-acetylcysteine prevents cellular injury after a reperfusion injury. No information is available regarding the neuroprotective potential of the free radical scavenger N-acetylcysteine after transient forebrain ischemia. In this study we evaluated the potential of N-acetylcysteine to improve hippocampal neuronal survival after transient forebrain ischemia in the rat. METHODS: In series A and B, ventilated, paralyzed, normothermic rats had 10 minutes of transient forebrain ischemia induced by bilateral carotid occlusion with hypotension induced by blood withdrawal (mean arterial blood pressure, 45 mm Hg). In series A, animals were administered N-acetylcysteine (163 mg/kg) 30 minutes and 5 minutes before transient forebrain ischemia. In series B, N-acetylcysteine (326 mg/kg) was administered 15 minutes after transient forebrain ischemia. In series C, N-acetylcysteine (326 mg/kg) was administered 15 minutes after transient forebrain ischemia in animals with a mean arterial blood pressure of 30 mm Hg during transient forebrain ischemia. All series had normal control, sham, and vehicle treatment groups. In all series, the rats were allowed to recover and were killed at 7 days after ischemia. The effect of forebrain ischemia was assessed by evaluating the number of viable neurons at bregma sections -3.3, -3.8, and -4.3 of the CA1 region of the hippocampus. RESULTS: The results demonstrated no physiological difference among the various treatment groups. There were no differences in the number of viable neurons between the transient forebrain ischemia with no treatment group and the vehicle (saline)-treated transient forebrain ischemic groups. Animals pretreated with N-acetylcysteine (mean number of neurons, 84 +/- 6) had a significant increase (P < .05) in neuronal survival compared with vehicle-treated animals (mean number of neurons, 43 +/- 4). Animals posttreated with N-acetylcysteine (mean number of neurons, 89 +/- 9) had a significant increase in neuronal survival compared with vehicle-treated animals (mean number of neurons, 7 +/- 1). However, N-acetylcysteine protection was only partial at 45 mm Hg and did not improve neuronal survival (mean number of neurons, 22 +/- 3) in animals with a more severe ischemic insult (mean arterial blood pressure, 30 mm Hg during transient forebrain ischemia) compared with vehicle-treated animals (mean number of neurons, 10 +/- 1). CONCLUSIONS: N-Acetylcysteine partially improved neuronal survival when administered before or after ischemia following transient cerebral ischemia (mean arterial blood pressure, 45 mm Hg) but not with a more severe ischemic insult of 10 minutes of transient cerebral ischemia with a mean arterial blood pressure of 30 mm Hg.

Acetylcysteine↗

PubMed1995

Beta 1-adrenoceptor subtype selective antagonism of esmolol and its major metabolite in vitro and in man. Investigations using tricresylphosphate as red blood cell carboxylesterase inhibitor.

Esmolol (CAS 103598-03-4, ASL-8052, Brevibloc) is an ultrashort acting beta-adrenoceptor antagonist which is rapidly hydrolyzed by a red blood cell esterase. In order to investigate the affinity profile of esmolol and its acid metabolite at beta-adrenoceptor subtypes in plasma and in whole blood in radioligand binding studies a potent esterase inhibitor was needed to prevent hydrolysis of esmolol and--in contrast to sodium fluoride--without influencing binding of the drugs at the receptor site. Tricresylphosphate was found to be a potent inhibitor of hydrolysis of esmolol which did not affect the parameters of radioligand binding. During an incubation time of 15 min at 25 degrees C in whole blood no significant metabolism of esmolol took place whereas without addition of inhibitor about 20% were inactivated. Thus, for the first time exact determinations of plasma concentrations of esmolol by ligand binding studies could be carried out. In vitro in radioligand binding studies esmolol had a 34 fold higher affinity for beta 1-adrenoceptors than for beta 2-adrenoceptors. Its acid metabolite had a very low and nonselective affinity for both adrenoceptor subtypes: Compared with esmolol it was 400fold less potent at beta 1-adrenoceptors. When plasma concentrations of esmolol and its metabolite after i.v. administration of esmolol to healthy volunteers (3000 micrograms/kg as a bolus and consecutively 500 micrograms/kg/min for 70 min) were determined in parallel by a beta 1-selective radioreceptor assay and an HPLC-method the following conclusions could be drawn from the direct correlation between the respective results: 1. (ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-1 Receptor Antagonists↗

PubMed1994

cAMP- and cGMP-dependent protein kinase phosphorylation sites of the focal adhesion vasodilator-stimulated phosphoprotein (VASP) in vitro and in intact human platelets.

The vasodilator-stimulated phosphoprotein (VASP) is a major substrate for cAMP-dependent- (cAK) and cGMP-dependent protein kinase (cGK) in human platelets and other cardiovascular cells. To identify the VASP phosphorylation sites, purified VASP was phosphorylated by either protein kinase and subjected to trypsin, V8 and Lys-C proteolysis. The phosphorylated proteolytic fragments obtained were separated by reversed phase high performance liquid chromatography. Sequence analysis of the phosphorylated peptides and 32P measurement of the released 32P-labeled amino acids revealed three phosphorylation sites: a serine 1-containing site (LRKVSKQEEA), a serine 2-containing site (HIERRVSNAG), and a threonine-containing site (MNAVLARRRKATQVGE). Additional experiments with purified VASP demonstrated that both cAK and cGK phosphorylated serine 2 rapidly and the threonine residue slowly, whereas cGK phosphorylated the serine 1 residue more rapidly than the cAK. These differences in the phosphorylation rates of VASP by the two protein kinases were also observed with synthetic peptides corresponding to the sequences of the three identified phosphorylation sites. These experiments also established the synthetic peptide serine 1 as one of the best in vitro cGK substrates and the serine 2-containing site as the site responsible for the phosphorylation-induced mobility shift of VASP in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Experiments with 32P-labeled platelets provided evidence that VASP is phosphorylated at the same three identified sites also in intact cells and that selective activation of cAK or cGK primarily increased the phosphorylation of both serine 2 and serine 1 but not threonine. Our results demonstrated overlapping substrate specificities of cAK and cGK in vitro and in intact cells. However, important quantitative and qualitative differences between cAK- and cGK-mediated phosphorylation of the focal adhesion protein VASP in human platelets were also observed, suggesting distinct functions of the two types of cyclic nucleotide-mediated VASP phosphorylation.

Amino Acid Sequence↗

PubMed1994

Dissecting differential binding in the forward and reverse reaction of Escherichia coli maltodextrin phosphorylase using 2-deoxyglucosyl substrates.

Substrate analogs are used in combination with site-directed mutagenesis to probe specific interactions between substrate and enzyme in the forward and reverse direction of the Escherichia coli maltodextrin phosphorylase reaction. In the phosphorolysis (degradation) mode, removal of the 2-OH group of the terminal glucose of the polysaccharide results in a 30-fold reduction of Km while similar changes were of no influence when the same polysaccharide was used for priming the synthesis. Mutation of active site residues Glu637 or Tyr538 does not change apparent affinity of substrates during degradation. In the synthesis mode, 2-deoxyglucose-1-P as substrate causes a 2-fold reduction of the wild-type kcat/Km while for the Y538F mutant a approximately 7-fold reduction is observed. In contrast, the mutation of Glu637 to Asp causes a 10-fold increase in kcat/Km. Therefore, different binding sites for the terminal glucose residue of the oligosaccharide and glucose-1-P exist. Glu637 and Tyr538 are part of the glucose-1-P binding site and do not interact with the terminal glucose residue. A 2-fold increase in rate was observed in both directions using the 2-deoxy derivatives. This confirms the role of intrinsic electronic effects in stabilizing the transition state. Uncompetitive substrate inhibition at high concentrations of maltoheptaose in the phosphorolysis direction is explained by inhibitory binding of the sugar in the synthesis mode.

Amino Acid Sequence↗

PubMed1994

Esmolol, an ultrashort-acting, selective beta 1-adrenoceptor antagonist: pharmacodynamic and pharmacokinetic properties.

The effects of esmolol at different rates of infusion (100, 250 and 500 micrograms.kg-1 BW.min-1) were compared with beta-adrenoceptor occupancy (beta 1 and beta 2, estimated by a subtype selective radioreceptor assay) and plasma concentrations of esmolol and its acid metabolite were measured by HPLC. Up to a rate of infusion of esmolol of 500 micrograms.kg-1 BW.min-1 there was a maximal beta 1-receptor occupancy of 84.7% while beta 2-receptor occupancy was below the detection limit; confirming the beta 1 selectivity of esmolol. Exercise-induced increases in heart rate and systolic blood pressure were reduced by esmolol in a dose-dependent manner. The estimated EC50 values of rate of infusion for the reduction in heart rate and systolic blood pressure during exercise were 113 and 134 micrograms.kg-1 BW.min-1, respectively. Additionally, heart rate and systolic blood pressure were reduced moderately at rest. Because of the short elimination half-life of esmolol caused by the rapid hydrolysis to its acid metabolite, 45 min after end of infusion high plasma concentrations of the metabolite (maximally 80 micrograms.ml-1) but no esmolol were detectable. Since no in vivo effects have been observed, despite the presence of high plasma concentrations of the metabolite, the metabolite did not participate in the observed effects up to an infusion rate of esmolol of 500 micrograms.kg-1 BW.min-1. The plasma concentrations of antagonist detected by radioreceptor assay and plasma concentrations of esmolol detected by HPLC showed a good correlation (r = 0.97).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗

PubMed1994

The cognition-enhancing drug tenilsetam is an inhibitor of protein crosslinking by advanced glycosylation.

Non-enzymatic glycosylation of proteins, also called Maillard reaction, which occurs at an accelerated rate in diabetes, can lead to the formation of advanced glycosylation endproducts (AGEs). Tenilsetam (CAS 997: (+/-)-3-(2-thienyl)-2-piperazinone), a cognition-enhancing drug successfully used for treatment of patients suffering from Alzheimer's disease, when included in the Maillard reaction apparently inhibits protein crosslinking by AGEs in vitro. According to the mechanism proposed, Tenilsetam acts via covalent attachment to glycated proteins, thus blocking the reactive sites for further polymerisation reactions. A beneficial effect of Tenilsetam in Alzheimer's disease could come from the interference with AGE-derived crosslinking of amyloid plaques and a decreased inflammatory response by diminished activation of phagocytosing microglia.

Aging↗

PubMed1994

Dose-effect and pharmacokinetic-pharmacodynamic relationships of the beta 1-adrenergic receptor blocking properties of various doses of carvedilol in healthy humans.

OBJECTIVE: To evaluate the pharmacodynamic properties of carvedilol across a broad range of doses in relation to its enantiospecific kinetics and adrenergic receptor occupancies, relative to placebo and propranolol. METHODS: Twelve healthy male subjects were investigated on six separate occasions at least 1 week apart when they received either a single peroral dose of 40 mg propranolol, 12.5, 25, 50, or 100 mg carvedilol, or placebo. The subjects were extensively profiled at supine rest, and they underwent supine bicycle ergometry before and at 2, 4, 6, 9, 12, and 22 hours after dosing. At these time points blood was drawn for the high performance liquid chromatographic determination of the enantiomers of carvedilol and for the radioreceptor assay determination of alpha 1- and beta 1-adrenergic receptor binding and related concentrations. RESULTS: Carvedilol was confirmed to bind to beta 1-adrenergic receptors and (albeit to a lesser extent) to alpha 1-adrenergic receptors. Carvedilol furthermore attenuated the ergometric increase in heart rate in a closely dose-related fashion, which exemplified its beta 1-adrenergic receptor blocking effects. However, the basal efferent adrenergic drive might have been too low to show consistent alpha 1-blocking properties. The radioreceptor and enantiomer kinetics were proportional with dose. There was no indication that the overall kinetic behavior of contributing active metabolites would differ from that of the S(-)-enantiomer. On average, there was a smooth linear relationship between the ergometric treatment responses and log-transformed dose, log-transformed concentrations of the S(-)-enantiomer, and the radioreceptor assay derived beta 1-adrenergic receptor occupancies. CONCLUSION: The relative complexity of the kinetics of carvedilol (enantiospecific kinetics and dynamics, protein binding, and involvement of active metabolites) does not preclude relatively simple and straight-forward dose-effect and kinetic-dynamic relationships.

Administration, Oral↗

PubMed1994

Reproducibility and consistency of the responses to supine bicycle ergometry; evaluation in conjunction with beta 1-adrenoceptor occupancies.

A protocol is presented for supine bicycle ergometry in healthy subjects, which aims for a target increase of heart rate (HR = 140 beats min-1) after 4 min cycling under constant load. The required load is selected from a pre-study ergometry with stepwise increasing load. Repeated testing with this protocol was shown to yield highly reproducible ergometric HR-responses. Because of their high reliability, the ergometric endpoints and increments permit a highly sensitive comparison of beta 1-adrenoceptor antagonism across dose and time within a given compound. The relationship between the changes of the ergometric rise of HR and the beta 1-adrenoceptor occupancy (estimated from radioreceptor assay data) permits to evaluate the ergometric efficiency of different beta-adrenoceptor antagonists across time and doses and to identify eventual differences that do not relate primarily to the extent of beta 1-adrenoceptor antagonism itself.

Adolescent↗

PubMed1994

[Subtypes of muscarinic receptors--aspects of their physiologic significance for controlling heart rate in the human].

The cDNAs for five different muscarinic cholinoceptors have been cloned. The biochemical and physiological relevance of the m1, m2 and m3 receptors is understood in many aspects. The pharmacological defined M1, M2 and M3 related to antagonists binding studies closely correspond with those cloned. We compared effects of atropine and of the subtype selective M-cholinoceptor antagonists pirenzepine and AF-DX 116 in humans. Dose- or time-response curves have been established for heart rate. Plasma samples were drawn in parallel with the effect measurements and analysed for drug concentrations. Subtype-selective radioceptor assays of the samples served to estimate the respective receptor occupancy in vivo. After low dosis of pirenzepine (M1-selective blockade) a negative chronotropic effect on heart rate could be observed. After high doses of pirenzepine or atropine (M-unselective blockade) the wellknown tachycardia appeared in parallel with occupancy of both the M2 and M3 subtypes. AF-DX 116 induced a tachycardia without a decrease of salivary flow in agreement with its selectivity profile (M2 > M1 > M3). Gastric emptying was only slightly inhibited by AF-DX 116 but nearly completely by a very high dose of pirenzepine blocking M1-, M2- and M3-cholinoceptors. The negative chronotropic effect on heart rate of a low dose of pirenzepine (M1 selective) was multi-folded by pretreatment with isoprenaline but disappeared during bicycle exercise. The implications of the functional M cholinoceptor heterogeneity in humans revealed by antagonists are discussed according to its possible importance for the control of autonomous nerve system.

Atropine↗

PubMed1994

The need for health care reform in Nebraska.

This paper has identified some of the major health care problems in Nebraska. Although Nebraska does not face as many serious challenges as some other states, there is clearly a need for reform. For example, the health of our population is generally good, but many serious gaps exist, particularly for minority population groups. Per capita health care costs in Nebraska are only slightly below the national average, and out-of pocket costs for the average Nebraska family rank among the highest in the nation. In addition, Medicaid costs are exploding and create serious challenges to balancing the state's budget. Nearly 140,000 Nebraskans lack health insurance coverage and at least 90,000 others are underinsured. Many insurance policies limit or deny coverage to individuals with pre-existing medical conditions, deny coverage to individuals employed in certain occupations, and limit coverage for preventive services. "Cost shifting" continues to become more widespread, which significantly increases the number of small businesses that drop or reduce health insurance coverage for their employees. Finally, rural areas face some unique challenges related to their ability and capacity to provide services. There is a serious shortage of primary care physicians, mid-level practitioners, and many other allied health professionals. As a result, individuals, including a large elderly population, must travel long distances to obtain care. Many rural hospitals are under severe financial stress and some will close during the next five years. There appears to be an adequate supply of nursing home beds in rural areas, but many communities lack adequate in-home services.

Female↗

PubMed1993

Hydrocephalus decreases chloride efflux from the choroid plexus epithelium.

To explore the novel concept of intrinsic brain regulation of the choroid plexus (CP), we studied the function of the CP exposed to increased intracranial pressure (ICP). The function of the CP was evaluated by in vitro chloride (Cl-) efflux from isolated CP 21 days after kaolin induced hydrocephalus. The Cl- efflux was significantly decreased in animals with elevated intracranial pressure (rate constant, K = 0.024 +/- 0.001 s-1) and enlarged ventricles (K = 0.023 +/- 0.001 s-1) compared to sham animals (K = 0.031 +/- 0.001 s-1). In contrast, the Cl- efflux of CP from animals with normal ICP and ventricular size did not differ from sham animals. These results illustrate the first demonstration of regulation of the CP epithelial function with elevated ICP; they also suggest a brain-CP regulatory mechanism that alters CP function.

Animals↗

PubMed1993

Reaction of imidazole-citrate-deformed glycogen phosphorylase with amino acids.

Incubation of phosphorylase with L-valine in the presence of 0.4 M imidazole citrate results in a time-dependent decrease in the absorption of the enzyme-bound cofactor pyridoxal 5'-phosphate at 333 nm and the generation of a new absorption maximum at 415 nm which appears to be due to an enzyme-bound coenzyme-amino-acid aldimine adduct. Consequently, the enzyme is inactivated to less than 10% of its initial activity. The formation of the adduct of phosphorylase b with L-valine (0.1 M) proceeds with t1/2 approximately 8 min at pH 6.8 and 25 degrees C and is slightly inhibited by AMP. Phosphorylase a reacts five times more slowly than phosphorylase b. The decrease in enzymic activity is linked to the formation of the coenzyme-amino-acid adduct and is not due to resolution of the enzyme. Both the original absorption spectrum and phosphorylase activity are restored by gel filtration in the absence of L-valine and imidazole citrate. Similar reactions occur with other L-amino acids, an exception being L-cysteine which leads to resolution of the enzyme [Shaltiel, S., Hedrick, J. L. & Fischer, E. H. (1966) Biochemistry 5, 2108-2116]. No reaction is observed with D-amino acids or in the absence of imidazole citrate. Pyridoxal-reconstituted phosphorylase rapidly produces with amino acids not only the aldimine adduct but also a species absorbing at 318 nm. Enzyme-bound pyridoxal 5'-phosphate and pyridoxal exhibit a positive CD signal in the region of 333 nm; in contrast, the absorption bands of the coenzyme-amino-acid adducts at 415 nm and 318 nm are optically inactive. Neither pyridoxal-5'-phosphate-reconstituted nor pyridoxal-reconstituted phosphorylase in imidazole citrate catalyses any of the common pyridoxal-5'-phosphate-mediated reactions of amino acids, e.g. transamination, decarboxylation or racemization, thus testifying to the high degree of reaction specificity of phosphorylase.

Amino Acids↗

PubMed1993

Two sites in the third inner loop of the dopamine D2 receptor are involved in functional G protein-mediated coupling to adenylate cyclase.

Synthetic peptides, corresponding to the amino acid sequences of the N- and C-terminal parts of the 3rd intracellular loop of the dopamine D2 receptor, attenuate dopaminergic adenylate cyclase inhibition in membranes. Both peptides also activate directly GTPase activity in membranes. We suggest a functional model for G(i)-coupled receptors where two sites in the 3rd inner loop compose the links for the receptor-G protein interaction thus providing the tools for a selective and adjustable response. Functional coupling was not affected by a peptide representing the insert in the long form of the dopamine D2 receptor (D2(long)). The selectivity pattern of conventional G protein-linked receptors also sheds some light on the recently observed interaction of beta-amyloid protein precursor (APP) complexes with G proteins.

Adenylyl Cyclase Inhibitors↗

PubMed1993

Effect of pretreatment with the selective beta 1-adrenoceptor antagonist bisoprolol on the subsequent cardiovascular actions and beta-adrenoceptor subtype specific occupancy of celiprolol in healthy man.

The cardiovascular effects at rest and during exercise and beta 1- and beta 2-adrenoceptor occupancy following a single dose of 1200 mg celiprolol p.o. were investigated in 8 healthy subjects with or without pretreatment with a single dose of 20 mg bisoprolol p.o., using a placebo-controlled, 2-way cross-over design. The ergometric responses of heart rate (HR) and systolic blood pressure (SBP) after celiprolol were reduced to a similar extent as after bisoprolol, but the cardiovascular function at rest was affected in a different way: there was a rise in HR, clear enhancement of cardiac systolic performance, and a considerable drop in the estimated total peripheral vascular resistance, associated with median beta 1-RRA and beta 2-RRA occupancies of 88 and 34%, respectively. The cardiovascular effects of celiprolol were not affected by pretreatment with bisoprolol. Celiprolol thus binds extensively to beta 1-adrenoceptors, moderately to beta 2-adrenoceptors, acts as beta 1-adrenergic antagonist (exemplified by the ergometric effects) but has vasodilator, positive chronotropic and cardiac systolic performance enhancing properties, which do not involve either direct or indirect beta 1-adrenergic agonism, but which might reflect beta 2-adrenergic agonism.

Adult↗

PubMed1992

Pyridoxal 5'-phosphate as a 31P reporter observing functional changes in the active site of Escherichia coli maltodextrin phosphorylase after site-directed mutagenesis.

Changes in the active site of Escherichia coli maltodextrin phosphorylase created by substituting residues Lys533, Arg534, Tyr538, and Glu637 were monitored in the absence and presence of arsenate as substrate analogue using pyridoxal-P as 31P NMR reporter. The chemical shift of the cofactor phosphate group of wild-type E. coli phosphorylase is pH dependent with an apparent pK of 5.6 and limiting delta values of 0.71 and 3.6 ppm for the low- and high-pH values, respectively. The apparent pK value of 5.6 indicates that the phosphate group of the cofactor is in hydrogen bond linkage to Lys533. In all mutant enzymes in which the enzymatic activity was significantly reduced, effects on the 31P chemical shift pattern of pyridoxal-P were observed. The K533S, R534Q, E637D, and E637Q mutant enzymes show 0.6, 0.01, 0.2, or 0.1% residual activity, and the apparent pK values of the cofactor phosphate transition of E637D and E637Q mutant enzymes are altered. The Y538F mutant enzyme is a remarkable exception, displaying 12% activity and an environment of the cofactor quite similar to that in wild-type enzyme. This finding suggests that Tyr538, although involved in substrate binding and specificity, is not functionally essential. One crucial aspect of catalysis is the close contact of the phosphates of pyridoxal-P and of substrate rendered by a cluster of positively charged amino acids, Lys533, Lys539, and Arg534. The similar apparent pK values of wild-type and K533S mutant phosphorylase suggest that the cofactor phosphate and the hydroxyl group of Ser533 are linked by a hydrogen bond.(ABSTRACT TRUNCATED AT 250 WORDS)

Arsenates↗

PubMed1992

Characteristic EEG findings in childhood moyamoya syndrome.

Moyamoya syndrome-specific alterations of EEG recordings are only observed in children. These consist of a gradual frequency decrease and amplitude activation after hyperventilation. This is referred to as re-build-up phenomenon. Thus, a tentative diagnosis of Moyamoya syndrome in children can be based on the EEG finding. This should be radiologically confirmed by angiography.

Cerebral Angiography↗