PubMed Health⌕ Search

Biomedical subjects

C Gerth

Publications and source records attributed to C Gerth.

At least 37 records · Page 2Linked to original sources
PubMed1990

Phosphofructokinase from Plasmodium berghei: a kinetic model of allosteric regulation.

As in mammalian cells, phosphofructokinase (PFK) is of major regulatory importance in the glucose metabolism of Plasmodium berghei. The malarial enzyme shows allosteric properties similar to PFK from various sources; it is activated by fructose-6-phosphate and inhibited by ATP, but differs with respect to allosteric regulation. Enzyme activity is only marginally increased by AMP, a potent activator of many phosphofructokinases. Phosphoenolpyruvate, which is reported to inhibit PFK activity, efficiency activates the malarial enzyme. No activation by ADP was observed. Instead, ADP inhibits the enzyme non-allosterically and competitively to the substrate MgATP. Phosphate stimulates the catalytic activity of malarial PFK independently of the activation by F6P and PEP.

Adenosine Diphosphate↗
PubMed1990

Regulation of the energy metabolism of Plasmodium berghei.

Energy metabolism of malaria parasites was investigated in P. berghei infected red blood cells of rat. Although Plasmodia contain mitochondria most of their ATP is formed by glycolysis. Lactate formation is two orders of magnitude higher than in noninfected erythrocytes. The coupling of respiration and glycolysis is very loose, a Pasteur-effect was not found. The key enzymes of glycolysis hexokinase and phosphofructokinase have been partially purified and kinetically characterized. The kinetic properties of both enzymes significantly differ from those of erythrocytes. They are less efficiently inhibited and PFK is activated only by PEP, Fru6P and Pi. The high rate of glycolytic proton formation in Plasmodia inhibits the PFK and thus the anaerobic energy metabolism of the host cell but not that of the parasite. Nevertheless the ATP concentrations in the host and the parasite compartment were found to be nearly identical. This supports the assumption that the parasites make ATP available to their host cell, probably by an adenine nucleotide translocator.

Adenosine Triphosphate↗
PubMed1990

Nucleotide status in erythrocytes of rats infected with Pl. berghei.

Nucleotide concentrations in erythrocytes of rats infected with Plasmodium berghei were measured by ion-pair reversed-phase HPLC. UTP and GTP levels were higher in highly infected red blood cells obtained after density separation. The infected red blood cells possess higher hypoxanthine, adenine, and adenosine levels.

Animals↗
PubMed1988

A kinetic model of phosphofructokinase from Plasmodium berghei. Influence of ATP and fructose-6-phosphate.

Phosphofructokinase (PFK) from the malarial parasite Plasmodium berghei shows the following kinetic features: the more the pH is decreased, the more the enzyme is inhibited by ATP; in contrast to PFK from erythrocytes, this inhibition is less potent by two orders of magnitude; as in the red cell, fructose-6-phosphate (F6P) is a positive effector. Kinetic modelling of PFK from P. berghei has been performed by taking the pH-dependence of activity into regard, implicitly by the estimation of pH-dependent kinetic parameters for the inhibition by ATP and the activation by F6P and explicitly by the assumption of protonation-steps involved in allosteric regulation. By means of a novel procedure of model discrimination [D. Buckwitz and H.-G. Holzhütter: A new method to discriminate between enzyme-kinetic models. In: Application of Computational Methods in Medicine (Györi, I., ed.), Akademai, Budapest, in press] we have selected among several kinetic models the best rate equation which provides an adequate quantitative description of the kinetic behaviour of the enzyme in the relevant ranges of substrate concentrations and pH (5.8-7.6). It thus becomes clear how the highly increased glycolytic flux in malaria-infected cells could be affected through PFK.

Adenosine Triphosphate↗
PubMed1987

Heterogeneity of glucose-6-phosphate dehydrogenase enzymopathies in the GDR.

G6PD variants of 13 patients from 12 German families with different clinical symptoms have been characterized kinetically. Vmax G6PD was nearly zero in red blood cells of all carriers. Therefore G6PD variants were isolated from leucocytes, which proved to be a suitable source for analysis of instable G6PD variants. The testing program included KmG6P, KmNADP, Ki values of NADPH, ATP and 2,3 P2G, rate of utilization of dG6P, Gal6P, dNADP, NAD, and pH dependence. From the results obtained one can conclude that all analyzed G6PD variants represent individual mutations. The degree of metabolic dysregulation can be explained by the different kinetic and physico-chemical properties of these G6PD variants.

Erythrocytes↗
PubMed1985

[Histomoniasis in pullet stock and its effect on later laying performance].

In a 17 1/2 weeks old pullet stock typhlohepatitis was diagnosed on the occasion of a stock examination by the poultry health service. Liver and gut of randomly selected pullets showed gross and histologic alterations as known in cases of typhlohepatitis in turkeys. Histomonads could be shown using both the PAS-reaction according to McManus and the silverstaining according to Grocott. In the following controls of the herd macroscopic visible alterations of the liver could not be seen, but some of the animals still exhibited gross lesions in the ceca. The course of the development of the herd from point-of-lay to the 9th month of laying period is described.

Animals↗
PubMed1983

[Effect of an alternating magnetic field on development and extinction of conditioned responses in rats].

This paper deals with the problem whether there is an effect of extremely low frequency electromagnetic fields on simple learning processes. The conditioned reaction upon an electromagnetic fields on simple learning processes. The conditioned reaction upon an acoustic stimulus (1000 Hz) reinforced by an electric painful stimulus was used. During the conditioning and extinction process 28 adult albino rats were put in a 10 Hz, 0,3 G magnetic field. Their learning and extinction behaviour was compared with that of a control group of 28 rats trained under normal laboratory conditions. The extinction schedule differs significantly between the experimental and control group: The extinction develops faster in the experimental group (p less than 0.05). In connection with the results of other authors our findings are discussed as a general amount of adaptability by the influence of the 10 Hz field.

Animals↗
PubMed1983

Mathematical model of pyruvate kinase of chicken erythrocytes.

The PK in mammals is different with regard to molecular structure and kinetic properties from PK in avian hepatocytes (1). Our studies show that the same isoenzyme of PK occurs both in red blood cells and hepatocytes. The PK of human erythrocytes belong to the L-type, that of chicken erythrocytes to the K-type. Both isoenzymes are characterized by cooperative regulation. Allosteric behavior is more pronounced for the chicken enzyme than for that of human erythrocytes. Chicken erythrocyte PK is activated by serine and exhibits a high FDP affinity.

Animals↗
PubMed1981

Identification of mutants of pyruvate kinase from red blood cells by means of trypsinization, electrophoresis, kinetic properties and immunological methods.

Enzymopathies of pyruvate kinase (PK) are characterized by polymorphism. 11 different mutants of PK were detected in 12 analysed cases. The frequency of double heterozygotes of the PK deficiency is very high. The mutant forms have been identified by electrophoretic, kinetic and immunologic methods in red blood cells of patients and members of their families. The effect of trypsin has greatly increased the sensitivity of the differentiation procedures. Differences in activity and quality of the proteolytic systems in liver and kidney in comparison to red blood cells are responsible for inactivation and degradation of PK mutants in both organs. Homozygotes and double heterozygotes show clinic manifestations. The rigidity of red blood cells increases with the severity of the nonspherocytic haemolytic anaemia.

Erythrocytes↗
PubMed1980

[Identification of pyruvate kinase variants from red blood cells using trypsinization and electrophoresis].

Enzymopathies of pyruvate kinase (PK) are characterized by polymorphism. Nine distinct variants of the L-type from 10 patients suffering from nonspherocytic haemolytic anaemia have been identified by electrophoretic and kinetic methods. Typical changes of the electrophoretic mobility and kinetic properties of the L-type and K-type of PK can be produced by incubation of cytolysates and tissue homogenates in the presence of trypsin. After trypsinization the three distinct forms of the L-type from liver and erythrocytes show identical mobility. Trypsinization of haemolysates has proved to be a diagnostic tool for the differentiation of PK variants. The results also allow to distinguish whether the mutation is located in the region of the peptide chain which is split off by trypsin or not. In three cases the occurrence of two instead of one enzyme form after trypsinization indicates a double heterozygote heredity of PK-deficiency. The appearance of the K-type isoenzyme of PK in red blood cells may be considered as a physiological event during a limited period of erythropoiesis. The K-isoenzyme was found only in samples of red blood cells containing erythroblasts. One of the patients has shown a still unknown form of PK. The properties of this form resembled those of the major part of PK from human placenta.

Anemia, Hemolytic, Congenital Nonspherocytic↗
PubMed1977

[Control of glycolysis in magnesium deficiency: studies on intact red cells and hemolysates].

The behaviour of glycolytic flux and glycolytic metabolic concentrations was studied under conditions of magnesium deficiency. The Mg-deficiency was produced in whole animals (rats) by feeding a diet almost completely free of Mg and in hemolysates of men by the addition of a chelating agent. The results show that the decrease of the free Mg-level is diminished by partial destruction of ATP and 2,3-DPG. The analysis of the control strength of the overall flux leads to the conclusion that the decrease of the glycolytic rate is caused by an inhibition of the hexokinase-phosphofructokinase-control system. The decrease of the MgATP-Complex and free Mg++-level explains the diminished phosphorylation of glucose by the hexokinase. The ATP-inhibition of the phosphofructokinase is amplified by a small increase of free ATP-concentration and a simultaneous decrease of the Fru-6P-level. The increase of the PEP-level is caused by the diminished free Mg++ and MgATP-complex and does not demonstrate a larger control strength of the pyruvate kinase.

Adenosine Diphosphate↗
PubMed1977

[Energy metabolism of erythrocytes in pyruvate kinase enzymopathies].

Until now pyruvate kinase enzymopathies have been described only for red blood cells. On the basis of these results special structural properties of the erythrocyte PK was assumed, which are not yet totally established. PK defects may cause a nonspherocytic hemolytic anemia. This enzymopathy is characterized by a polymorphism, which is expressed in more than 5 different pathological variants. Up to now 16 cases of PK deficiency have ben diagnozed in the GDR. The following parameters are used for the characterization of the PK: the PEP-dependance, the inhibition by ATP and alanine, the specificity to nucleotides, the stability to temperature and urea and the maturation dependence. Two pathological variants of the PK with a decreased PEP-affinity are described. Furthermore the differences in the energy metabolism of the red blood cells of these two patients under aerobic and anaerobic conditions are discussed.

Adenosine Triphosphate↗
PubMed1976

Rheology of fibrin clots. III. Shear creep and creep recovery of fine ligated and coarse unligated closts.

Creep and creep recovery of human fibrin clots in small shearing deformations have been investigated over a time scale from 24 to 10(4) s. Coarse, unligated clots and fine clots ligated by fibrinoligase in the presence of calcium ions were studied to suppliement previous data on coarse ligated and fine unligated clots. Stress was found to be proportional to strain up to at least a maximum shear strain (in torsion geometry) of 6.2%. The initial modulus (25 s after imposition of stress) is proportional to approximately the 1.5 power of concentration for fine ligated and coarse unligated clots. For fine unligated closts there is comparatively little creep subsequent to the initial deformation; ligation (in this case involving mostly the gamma chains) reduces the creep to nearly zero. For coarse unligated clots, there is substantially more creep under constant stress, and creep recovery is not complete. Ligation (in this case involving both camma and alpha chains) alrgely supresses the creep and causes the recovery to be complete. If the structure if fully formed before creep begins, tests of creep recovery by the Boltzmann superposition principle show adherence to linear visoelastic behavior for all four clot types. Otherwise, the Boltzmann test fails and the recovery is much less than calculated. For fine ligated clots, the observed recovery agrees well with that calculated on the basis of a dual structure model in which an additional independent structure is built up in the deformed state, so that the state of ease after removal of stress is a balance between two structures deformed in opposite senses. It is postulated that the coherence and elastic modulus of the fine ligated clot are largely due to steric blocking of long protofibrils with a high flexural stiffness. In the coarse clot, it is proposed that the structure involves extensive branching of thick bundles of protofibrils, which become permanently secured by the ligation of the alpha chains of the fibrin.

Blood Coagulation↗