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Biomedical subjects

V Esmann

Publications and source records attributed to V Esmann.

At least 55 records · Page 3Linked to original sources
PubMed1978

The role of calcium and cyclic adenosine 3',5'-monophosphate in the regulation of glycogen metabolism in phagocytozing human polymorphonuclear leukocytes.

Incubation of human polymorphonuclear leukocytes in a glucose-free Krebs-Ringer bicarbonate buffer for 2 h resulted in glycogen depletion, decreased phosphorylase activity and increased synthase-R activity. Addition of dialyzed latex particles to starved leukocytes revealed a very rapid ingestion rate (half-maximal ingestion within 30 s). This uptake is followed by glycogenolysis associated with an immediate two-fold increase in phosphorylase a activity and a synthase-R to -D conversion within 30 s. Furthermore, in rapid time-course experiments with phagocytozing cells we found that the concentration of cyclic AMP increased by 93% within 15 s and returned to baseline values at 1 min. In a medium without added calcium and with 1 mM ethyleneglycol-bis-(beta-aminoethylether)-N,N'-tetraacetic acid, phagocytosis was blocked, cyclic AMP formation decreased by 50% and phosphorylase activation was abolished, but the conversion of synthase-R to -D was preserved. Addition of calcium ions to cells suspended in a calcium-free buffer without added latex results in phosphorylase activation and glycogenolysis, but not in cyclic AMP increase or synthase-R to -D conversion. Measurements of 45Ca efflux during phagocytosis suggest an initial increase in cytosolic calcium obtained by a release of membrane-bound 45Ca. Activation of phosphorylase during phagocytosis is thus presumably due to an increase in cytosol Ca2+ and subsequent activation of phosphorylase kinase, and is independent of the simultaneous increase in concentration of cyclic AMP. Phosphorylation of synthase R to the D form does not depend on the presence of Ca2+ in the extracellular phase.

Calcium↗
PubMed1978

Effects of catecholamines and glucagon on glycogen metabolism in human polymorphonuclear leukocytes.

Addition of 10 micron of the alpha-adrenergic agonist phenylephrine to polymorphonuclear leukocytes suspended in glucose-free Krebs-Ringer bicarbonate buffer (pH 6.7) activated phosphorylase, inactivated glycogen synthase R maximally within 30 s, and resulted in glycogen breakdown. Phenylephrine increased 45Ca efflux relative to control of 45Ca prelabelled cells, but did not affect cyclic adenosine 3',5'-monophosphate (cAMP) concentration. The effects of phenylephrine were blocked by 20 micron phentolamine and were absent in cells incubated at pH 7.4. The same unexplained dependency of extracellular pH was observed with 2.5 nM--2.5 micron glucagon, which activated phosphorylase and inactivated synthase-R, but in addition caused a 30-s burst in cAMP formation. 25 nM glucagon also increased 45Ca efflux. The activation of phosphorylase by phenylephrine and possibly also by glucagon are thought mediated by an increased concentration of cytosolic Ca2+ activating phosphorylase kinase. The effects of 5 micron isoproterenol or 5 micron epinephrine were independent of extracellular pH 6.7 and 7.4 and resulted in a sustained increase in cAMP, an activation of phosphorylase and inactivation of synthase-R within 15 s, and in glycogenolysis. The effects of both compounds were blocked by 10 micron propranolol, whereas 10 micron phentolamine had no effect on the epinephrine action. The efflux of 45Ca was not affected by either isoproterenol or epinephrine. The beta-adrenergic activation of phosphorylase is consistent with the assumption of a covalent modification of phosphorylase kinase by the cAMP dependent protein kinase. Phosphorylation of synthase-R to synthase-D can thus occur independently of increase in cAMP, but the evidence is inconclusive with respect to the cAMP dependent protein kinase also being active in this phosphorylation.

Calcium↗
PubMed1977

The hysteretic properties of glycogen synthase I.

Glycogen-free synthase I from human polymorphonuclear leukocytes is activated by its own substrate, glycogen, in a slow, time-dependent process (hysteretic activation). This lag in response to addition of glycogen depends on the concentration of glycogen, pH and temperature. At pH 7.4 and at a temperature of 30 degrees C, the half-time of activation t 1/2 decreases from 89 min at 0.004 mg/ml glycogen to 6 min at 25 mg/ml. The activation is accelerated by increasing temperature and pH, but is not influenced by enzyme concentration, glucose 6-phosphate, UDP, high ionic strength, EDTA, mercaptoethanol, glucose, sucrose or amylase limit dextrin. The Km for UDP-glucose (0.024 mM) and the activity ratio were unchanged during the activation process. The activation can be described by vt = vf + (vo - vf) e-kt where vt, vf and vo are velocities at times t, O and infinity and k is a complex rate constant. Evidence from ultracentrifugation and kinetic studies is presented to substantiate the hypothesis that the underlying mechanism is a simple biolecular process: enzyme + glycogen in equilibrium enzyme-glycogen complex, with the dissociation constant Ks = 0.003 mg/ml. The hysteretic activation may become rate-limiting during experiments in vitro with synthase. The possibility of a physiological role in glycogen metabolism, perhaps in the form of a concerted hysteresis with H+ is discussed.

Enzyme Activation↗
PubMed1976

Purification and steady state kinetic mechanism of glycogen synthase-D from human polymorpho-nuclear leukocytes.

The authors' work on the purification and steady state kinetic investigation of the enzyme glycogen synthase D (UDP-glucose: glycogen 4-alpha-glucosyl-transferase, EC 2.4.1.11) from human polymorphonuclear leukocytes is reviewed. The main features of the kinetic mechanism for catalysis of the reaction interconversion of the quaternary enzyme-substrate-activator complexes. The anions interact exclusively with the G-6-P binding site of the enzyme. The dissociation constants for the enzyme-modifier complexes are determined, and a kinetic mechanism for the action of the anions is proposed, leading to activation or inhibition, depending on the concentration of G-6-P.

Adenosine Triphosphate↗
PubMed1975

Lymphocyte ATP-ase activity in treated cases of Hodgkin's disease.

The ATP-ase activity was determined in lymphocytes isolated from peripheral blood in 41 patients with Hodgkin's disease and 50 healthy controls. All patients were previously treated with irradiation or cytostatic drugs and 17 patients were under maintenance therapy at the time of investigation. A significantly increased ATP-ase activity was found in lymphocytes from patients with Hodgkin's disease. The individual activities were unrelated to the clinical stage of the disease, but correlated to the histological classification of the lymphatic tissue. Significantly lower lymphocyte ATP-ase activity was found in patients under maintenance treatment with immunosuppressive drugs, especially if the patients had previously been irradiated. It is suggested that the ATP-ase activity of circulating lymphocytes is related to the immunological activity against the presence of the malignant cells in Hodgkin's disease.

Adenosine Triphosphatases↗
PubMed1975

Elevated lymphocyte ATP-ase activity in patients with cancer of the uterine cervix.

Elevated lymphocyte Adenosine Tri-Phosphatase (ATP-ase) activity was found in 23 och 28 patients with cervical uterine carcinomas of various stages. Treatment with external irradiation and radium insertion was followed by a decline in the lymphocyte ATP-ase activity in 22 patients, while the activity remained unchanged in one patient. No correlation between the tumour stage and the lymphocyte ATP-ase activity was demonstrated. In 24 patients the clinical effect of the treatment was well correlated with the decline in ATP-ase activity. It is suggested that the determination of lymphocyte ATP-ase activity could be valuable in screening for cervical carcinoma and for follow-up after radical treatment.

Adenosine Triphosphatases↗
PubMed1975

Inactivation of glycogen phosphorylase of human polymorphonuclear leukocytes.

Glycogen phosphorylase of human polymorphonuclear leukocytes is dephosphorylated during incubation of a gel-filtered cell extract. The dephosphorylated enzyme (b form) retains 25 per cent of the activity of the phosphoenzyme (a form) when measured without AMP but a high glucose-1-phosphate concentrations. The ratio of activity -AMP/+AMP for the a enzyme is 0.8-1.0 and for the b enzyme 0.2. Leukocyte phosphorylase is not activated by -SH groups, but the b enzyme is stimulated by 0.4 mol/1 Na2SO4. The phosphatase which catalyzes the conversion of phosphorylase a to b is inhibited by glucose-1-phosphate and AMP both a 14 degrees C and 25 degrees C. Glucose counteracts the AMP inhibition but not the glucose-1-phosphate inhibition at both temperatures. Glucose alone had no effect at 25 degrees C, but it accelerated the phosphatase reaction at 14 degrees C. Glucose-6-phosphate or glycogen alone or in the presence of AMP or glucose-1-phosphate did not affect the phosphatase reaction. From previous and present experiments it is concluded that the phosphorylase of human polymorphonuclear leukocytes is closely related to liver phosphorylase and that the inactivation of the enzyme is mainly controlled by AMP and glucose.

Adenosine Monophosphate↗