PubMed Health⌕ Search

Biomedical subjects

J U Becker

Publications and source records attributed to J U Becker.

At least 19 recordsLinked to original sources
PubMed1987

Pharmacokinetics of flecainide in patients with mild and moderate renal failure compared with patients with normal renal function.

We have studied the pharmacokinetics of flecainide after the oral administration of 100 mg to 8 patients without renal impairment and 8 patients with mild to moderate renal failure. Both groups gave comparable results with respect to the peak plasma concentrations and the time to peak. There was a significant correlation between renal flecainide clearance and endogenous creatinine clearance. The elimination half-time in the patients with impaired renal function was significantly longer (19.9, SD 9.9 h) than that in the patients with normal renal function (11.5, SD 4.2 h), but the variability in the elimination half-time in renal failure could not be explained on the basis of the available results.

Female↗
PubMed1986

[Hemoperfusion in flecainide poisoning].

A 79-year-old patient, who had received a pacemaker after suffering two posterior myocardial infarctions, was treated with 2 X 100 mg flecainide daily for 9 days for ventricular extrasystoles (Lown IV b). On admission to the hospital the parameters of renal function were within the normal range. Ten days after flecainide treatment was begun a temporary electromechanic decoupling of the pacemaker occurred with reversible asystoly and progressive kidney failure. The flecainide plasma level at that time was 1460 ng/ml. Hemoperfusion for 3 h with activated charcoal removed only 35 mg flecainide in spite of an excellent flecainide clearance (164-180 ml/min). The patient's flecainide plasma level did not decrease sufficiently during the procedure, showing clearly that flecainide levels cannot be lowered fast enough by hemoperfusion to treat a flecainide intoxication.

Aged↗
PubMed1984

[Determination of the concentration of a new antiarrhythmic, flecainide, in plasma using high pressure liquid chromatography (HPLC): sample preparation with extraction columns].

A method is described for the rapid determination of flecainid (Tambocor) in human plasma. Flecainid is removed from alkalized plasma by binding to a C-18 extraction column. After washing the column with methanol/water (1 + 1, by vol.) and acetonitrile/water (45 + 55, by vol.), the drug is extracted with methanol and determined by HPLC. Sample preparation takes about 15 minutes. With this method, flecainid can be determined directly in the concentration range 100-2000 micrograms/l, with an accuracy of 5-10% depending on the concentration. The results agree well with those obtained by the longer established but lengthy liquid extraction method.

Anti-Arrhythmia Agents↗
PubMed1983

Regulation of yeast phosphorylase by phosphorylase kinase and cAMP-dependent protein kinase.

Yeast phosphorylase is phosphorylated and activated by a cyclic AMP-independent protein kinase (called phosphorylase kinase) and a cyclic AMP-dependent protein kinase. Only in the presence of both kinases is phosphorylase fully activated and phosphorylated. No evidence was found for the presence of two phosphorylation sites as an identical phosphopeptide pattern of phosphorylase is obtained after phosphorylation by either one or both kinases. The kinases probably phosphorylate identical sites but recognize different subunits of phosphorylase. Phosphorylase kinase phosphorylates the high-Mr subunit while cAMP-dependent protein kinase phosphorylates the low-Mr subunit.

Enzyme Activation↗
PubMed1983

Characterization of phosphorylase kinase activities in yeast.

Two phosphorylase kinase activities were resolved by DEAE-cellulose chromatography. The main activity peak was enriched 2800-fold, the minor appeared to be an aggregate of the enzyme. Phosphorylase kinase also phosphorylated histone and casein with no changes in phosphorylation ratios throughout the preparation steps but was most active on yeast phosphorylase. The molecular weight was 29000 +/- 2000. ATP, UTP, GTP served as substrates while CTP was inactive. Mg-ions activated the kinase without inhibition at high concentrations (30 mM). In addition to this cAMP-independent kinase, cAMP-dependent protein kinase also phosphorylated phosphorylase. The catalytic subunit and phosphorylase kinase were not identical since the latter was not inhibited by yeast cAMP binding protein.

Cyclic AMP↗
PubMed1983

Characterization of phosphoprotein phosphatases and phosphorylase phosphatase from yeast.

Three peaks of protein phosphatase (phosphoprotein phosphohydrolase, EC 3.1.3.16) activity (fractions a, b and c) acting on muscle phosphorylase (1,4-alpha-D-glucan:orthophosphate alpha-D-glucosyltransferase, EC 2.4.1.1) were separated by DEAE-cellulose chromatography of yeast extracts. In contrast to fractions a and b, only fraction c was able to liberate phosphate from 32P-labelled inactivated yeast phosphorylase. The activity of fraction c on both substrates was totally dependent on the presence of bivalent metal ions (Mg2+, Mn2+), and was activated by Mg . ATP. Following freezing in the presence of mercaptoethanol, fractions a and b were also able to dephosphorylate yeast phosphorylase. Rabbit muscle phosphoprotein phosphatase inhibitors 1 and 2 showed that yeast phosphatases acting on muscle phosphorylase were inhibited by inhibitor 2 but not by inhibitor 1. The action of fraction c on yeast phosphorylase was not inhibited by either inhibitor. The native yeast phosphorylase phosphatase (EC 3.1.3.17) was purified 8000-fold by ion-exchange chromatography, casein-Sepharose chromatography and Sephadex G-200 gel filtration. The purified enzyme was unable to dephosphorylate rabbit muscle phosphorylase a, but acted on casein phosphate (Km 3.3 mg/ml). Molecular weight was estimated to be 78 000 and pH optimum 6.5-7.5. Activity of the enzyme was dependent on bivalent metal ions (Mg2+, Mn2+) and was inhibited by fluoride (Ki 20 mM) and succinate (Ki 10 mM).

Kinetics↗
PubMed1983

Purification and properties of phosphorylase from baker's yeast.

A rapid, reliable method for purification of phosphorylase, yielding 200-400 mg pure phosphorylase from 8 kg of pressed baker's yeast, is described. The enzyme is free of phosphorylase kinase activity but contains traces of phosphorylase phosphatase activity. Phosphorylase constitutes 0.5-0.8% of soluble protein in various strains of yeast assayed immunochemically. The subunit molecular weight (Mr) of yeast phosphorylase is around 100,000. The enzyme is composed of two subunits in various ratios, differing slightly in molecular weight and N-terminal sequence. Both are active. Only the enzyme species containing the larger subunit can form tetramers and higher oligomers. The activated enzyme is dimeric. Correlated with specific activity (1 to 110 U/mg), phosphorylase contained between less than 0.1 to 0.74 covalently bound phosphate per subunit. Inactive forms of phosphorylase could be activated by phosphorylase kinase and [gamma-32P]ATP with concomitant phosphorylation of a single threonine residue in the aminoterminal region of the large subunit. The small subunit was not labeled. The incorporated phosphate could be removed by yeast phosphorylase phosphatase, resulting in loss of activity of phosphorylase, which could be restored by ATP and phosphorylase kinase.

Enzyme Activation↗
PubMed1982

Flux regulation in glycogen-induced oscillatory glycolysis in cell-free extracts of Saccharomyces carlsbergensis.

To localise the controlling point of the glycolytic system, the temporal changes in concentrations of glycolytic intermediates have been analysed after addition of glycogen to a substrate-depleted yeast extract. Three sequential metabolic states are clearly observable: a transition state at which there is continuous accumulation of the intermediates before the glyceraldehydephosphate dehydrogenase (GAPDH, EC 1.2.1.12) step; a stationary state with all glycolytic intermediates having concentrations oscillating at nearly stationary mean values; and a depletion state at which the intermediates before the GAPDH step are being depleted due to the exhaustion of glycogen. In all these states, the mean ethanol production rate and the concentration of ATP and the intermediates beyond the GAPDH-step are maintained fairly constant, while the glycogen consumption rate and intermediate concentrations of the upper part of the glycolytic system changes considerably: the glycogen consumption rate varies 4-fold and fructose-bis-phosphate concentration more than 10-fold. Doubling of the initial glycogen concentration and the addition of a great excess of fructose-bis-phosphate do not affect the ethanol production rate and the mean glycerate-3-phosphate (3-PGA) and pyruvate levels. By contrast, ethanol production was accelerated by an increase of the net ATP consumption rate resulting from either the addition of apyrase or by substitution of trehalose for glycogen. Neither the mean absolute ATP level nor the adenylate energy charge were measurably affected, however, all this data can be interpreted in terms of a very strong stoichiometric regulation and stabilization of the lower part of the glycolytic system.

Adenosine Triphosphate↗
PubMed1982

Mechanisms of regulation of glycogen phosphorylase activity in Saccharomyces carlsbergensis.

The content of glycogen phosphorylase (1,4-alpha-D-glucan: orthophosphate alpha-D-glycosyl-transferase, EC 2.4.1.1) in yeast (Saccharomyces carlsbergensis) cells depended on the growth phase. Cells of the early exponential phase under carbohydrate-limited conditions showed low, but significant, phosphorylase activity; the activity markedly increased in the late exponential growth phase, concomitant with the appearance of measurable phosphorylase antigen. This pointed to an induction of the enzyme. During the interexponential phase (the slow proliferation phase during the diauxic growth of the culture, when the cells switch to utilization of accumulated ethanol) and the stationary growth phase, phosphorylase concentration remained constant while its specific molecular activity increased further, probably caused by conversion of the enzyme to an active form. During transition of stationary phase cells to growth, phosphorylase activity and concentration slowly decreased in the cells at a rate compatible with dilution by newly synthesized proteins. A residual activity always remained, which could be attributed to the presence of active phosphorylase, detectable by activity staining after gel electrophoresis in the presence of glycogen. No direct correlation could be detected between the specific molecular activity of phosphorylase and glycogen metabolism. This indicated that covalent modification of the enzyme regulated the total capacity of the enzyme available to the cell, rather than the actual activity limiting glycogen breakdown.

Carbohydrate Metabolism↗
PubMed1979

1,4-alpha-Glucan phosphorylase from the slime mold Physarum polycephalum. Purification, physico-chemical and kinetic properties.

Glycogen phosphorylase from macroplasmodia of Physarum polycephalum was purified 76-fold to homogeneity. The native enzyme migrated as a single protein band on analytical disc gel electrophoresis coinciding with phosphorylase activity. After reduction in the presence of sodium dodecylsulfate one protein band was detectable which corresponded to an Mr of 93 000. The molecular weight of the native enzyme determined by gel sieving or gradient-polyacrylamide gel electrophoresis was 172000 and 186000, respectively. The enzyme contained about 1 mol pyridoxal 5'-phosphate and less than 0.1 mol covalently bound phosphate per mol subunit. The amino acid composition of the enzyme was determined. In the direction of phosphorolysis the kinetic data were determined by initial velocity studies, assuming a rapid equilibrium random mechanism. Glucose 1-phosphate and GDP-glucose were competitive inhibitors toward phosphate and noncompetitive to glycogen. 5'-AMP, a weak activator of the enzyme, counteracted the glucose-1-phosphate inhibition completely. Physarum phosphorylase was compared with phosphorylases from other sources on the basis of chemical and kinetic properties. No evidence for the presence of phosphorylated forms has yet been found.

Adenosine Monophosphate↗
PubMed1979

Partial purification, substrate specificity and regulation of alpha-L-glycerolphosphate dehydrogenase from Saccharomyces carlsbergensis.

alpha-L-Glycerolphosphate dehydrogenase (sn-glycerol-3-phosphate:NAD+ 2-oxidoreductase, EC 1.1.1.8) from Saccharomyces carlsbergensis was purified 400-fold. The enzyme preparation is free of interfering activities, such as glyceraldehyde phosphate dehydrogenase, alcohol dehydrogenase, triose phosphate isomerase and glycerolphosphatase. At pH 7.0 it is specific for NADH (Km = 0.027 mM with 0.8 mM dihydroxyacetone phosphate) and dihydroxyacetone phosphate (Km = 0.2 mM with 0.2 mM NADH). Between pH 5.0 and 6.0 the enzyme functions with NADPH, but only at 7% of the rate with NADH. Various anions (I- greater than SO42- greater than Br- greater than Cl-) act as inhibitors competing with the substrate dihydroxyacetone phosphate. Inorganic phosphate (Ki = 0.1 mM), pyrophosphate and arsenate are strong inhibitors. The nucleotides ATP and ADP are also inhibitory, but their action seems to be of the same type as the general anion competition (Ki = 0.73 mM for ATP). The results are consistent with the notion that the enzyme may regulate the redox potential of the NAD+/NADH couple during fermentation.

Adenine Nucleotides↗
PubMed1977

Glycogen synthase in Saccharomyces carlsbergensis cells capable of oscillatory glycolysis.

1. Saccharomyces carlsbergensis cells were found to store about 10% of the glucose taken up as glycogen during oscillatory glycolysis. 2. Under the same conditions and during all phases of carbohydrate limited growth, glycogen synthase (E.C. 2.4.1.11), in the absence of glucose 6-phosphate, had only 5--20% activity compared to the activity in the presence of 10 mM of the effector, indicative for the D-form of the enzyme. 3. Inorganic phosphate (intracellular concentration 19--23 mumoles/g yeast) strongly inhibited glycogen synthase both in the absence of glucose 6-phosphate and competitively to this effector. 4. In this yeast, the D-form of glycogen synthase had to be active to account for the high rate of glycogen synthesis. The resulting sensitivity to glucose 6-phosphate may lead to a pulsatory action of the enzyme during oscillatory glycolysis.

Cell-Free System↗
PubMed1977

Purification and properties of debranching enzyme from dogfish muscle.

Glycogen debranching enzyme (4-alpha-glucanotransferase amylo-1,6-glucosidase, EC 2.4.1.25 + 3.2.1.33) was purified 140-fold from dogfish muscle in a rapid, high-yield procedure that takes advantage of a strong binding of the enzyme to glycogen, and its quantitative adsorption to concanavalin A-Sepharose only when the polysaccharide is present. The final product was hrophoresis in the presence and absence of dodecyl sulfate. A molecular weight of 162,000 +/- 5000 was determined by sedimentation equilibrium analysis in good agreement with the value of 160,000 estimated by gel electrophoresis, but a low-sedimentation constant of 6.5 S suggests that the enzyme is asymmetric. The molecule appears to be made up of a single polypeptide chain with no evidence for multiple repeating sequences: it could not be dissociated into smaller fragments by dodecyl sulfate even after complete carboxymethylation; tryptic cleavage of the native protein yielded only two fragments of molecular weight 20,000 and 140,000 without loss of enzymatic activity. The amino acid composition of the enzyme is reported; no covalently bound phosphate or carbohydrate could be detected. All 32 sulfhydryl groups present were titrated with 5,5'-dithiobis(2-nitrobenzoic acid) under denaturing conditions; eight reacted readily in the native enzyme without loss of catalytic activity, while substitution of eight additional ones lowered the activity by 50%. Inactivation was greatly reduced by glycogen; the polysaccharide also influenced markedly the electrophoretic behavior of the enzyme and large filamentous aggregates were formed when solutions of both were mixed. Purified debranching enzyme releases 3 mumol of glucose min-1 mg-1 at 19 degrees C, pH 6.0, from a glycogen limit dextrin and one-tenth this amount when the native polysaccharide is used as substrate; glycogen is quantitatively degraded in the presence of phosphorylase. None of the usual sugar phosphates or nucleotide effectors of glycolysis affected enzymatic activity. No phosphorylation by either dogfish or rabbit skeletal muscle protein kinase or phosphorylase kinase could be demonstrated, nor any direct interaction with phosphorylase as measured by SH-group reactivity, enzymatic activity, or rate of phosphorylase b to a conversion. Purification of the 160,000 molecular weight M-line protein of skeletal muscle resulted in the quantitative removal of debranching enzyme, indicating that the two proteins are different.

Amino Acids↗