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Biomedical subjects

E Hofmann

Publications and source records attributed to E Hofmann.

At least 181 records · Page 10Linked to original sources
PubMed1985

Temporal organization of the phosphofructokinase/fructose-1,6-biphosphatase cycle.

The dynamic and functional organization of the fructose-6-phosphate/fructose-1,6-bisphosphate cycle has been investigated in an open and homogeneous reconstituted enzyme system containing phosphofructokinase, fructose-1,6-biphosphatase, pyruvate kinase, adenylate kinase and glucose 6-phosphate isomerase. The properties of this system were analyzed by a model based on the kinetic properties of the individual enzymes. It could be shown that in a broad parameter region sustained oscillations arise. At low maximum activities of phosphofructokinase a domain of multiple stationary states occurs, in which stable stationary states can coexist with a stable oscillatory or with an alternate stable stationary state. The occurrence of oscillations and the emergence of alternate stationary motions are caused mainly by the reciprocal effect of the allosteric effectors AMP and fructose-2,6-bisphosphatase must be involved in the reaction network. The study of bisphosphatase. The attained states can either be glycolytic or gluconeogenic, their metabolic efficiencies depend mainly on the maximum activities of phosphofructokinase and fructose-1,6-bisphosphatase as well as on the supply of fructose-6-phosphate and fructose-1,6-bisphosphate. Efficient metabolic states arise only when both the enzyme concentrations and the rates of substrate supply favor either the glycolytic or the gluconeogenic mode of action. At medium maximum concentrations of the enzymes oscillations occur, in which glycolytic and gluconeogenic states are consecutively passed. A high rate of substrate cycling is observed only at the transitions between the functionally antagonistic phases of the periodicities. By this temporal organization the mean efficiency of the states is increased. The integration of fructose-2,6-bisphosphate as very sensitively acting activator of phosphofructokinase and inhibitor of fructose-1,6-bisphosphatase gives rise either to emergence of oscillations or of their extinction. Generally, the glycolytic mode is favored by this effector because of its stimulatory action on the phosphofructokinase activity.

Fructose-Bisphosphatase↗
PubMed1985

[Central traumatic cerebral hemorrhage in the computed tomogram].

Traumatically caused central brain haemorrhages are relatively rare. From 1976 through 1984 3598 patients were submitted to computed tomography examination in our department after craniocerebral trauma. Central lesions could only be found in about 3% of the injured. They generally occurred in combination with other severe damage of the skull and skull contents. Most frequently, such central haemorrhages could be found in the basal ganglia occasionally extending into the adjacent medullary layer resulting in large intracerebral haematoma. The right hemisphere was affected significantly more frequently and more severely by such large-size haemorrhages than the left hemisphere. The thalamus region ranking second in localisation of central traumatic haemorrhages was virtually never found to be the origin of large haematomas. In general, no definite distinction could be made between primary and secondary traumatic haemorrhages. We identified, however, a few cases of purely central bleeding without accompanying brain lesions. These haematomas, which were most probably caused primarily by trauma, as well as those with associated damage, preferred the regions of basal ganglia and thalamus. The prognosis of central brain haemorrhages was relatively poor with a 42% lethality rate. However, it depended on the severity of the accompanying brain lesions. Thus, isolated central haemorrhages even had a markedly favourable prognosis. The number of survivors of central bleeding turned out to be approximately the same as the number of deaths, the ratio thus being 1:1. Nevertheless, we think that especially small lesions occur more frequently and have a better survival rate than had been supposed up to now.

Basal Ganglia↗
PubMed1985

An electron microscopy study of the quarternary structure of yeast phosphofructokinase.

Homogeneous phosphofructokinase from yeast with a molecular weight of 835 000 and composed of eight subunits (four alpha and four beta subunits) was examined by electron microscopy and image computer processing. Three types of particles were seen representing different projections of the phosphofructokinase molecule. A structural model of the enzyme was developed, each of the subunits having two oblong "domains" with a length of 8 and 4.5 nm, respectively. The smaller "domain" is attached to the center of the larger one. One alpha and one beta subunit are regarded to form a heterodimer. Four heterodimers (alpha beta) are tetrahedrally assembled giving rise to point group symmetry 222.

Computers↗
PubMed1985

Interaction of ADP and fructose-2,6-bisphosphate with phosphofructokinase-1 from yeast.

ADP was found to activate or, depending on the experimental conditions, to inhibit yeast phosphofructokinase-1. In the absence of AMP and fructose-2,6-bisphosphate ADP increases the apparent affinity of the enzyme to fructose-6-phosphate. At low ATP concentrations the maximum activity with respect to fructose-6-phosphate decreases in the presence of ADP, while at high ATP a significant increase of the maximum activity by ADP is observed. In the presence of fructose-2,6-bisphosphate and AMP only the inhibiting effect of ADP persists. The data may be interpreted in terms of a hyperbolic inhibition mechanism.

Adenosine Diphosphate↗
PubMed1985

Inorganic phosphate amplifies the effects of AMP and fructose-2,6-bisphosphate on yeast phosphofructokinase.

Inorganic phosphate is an important regulator of yeast phosphofructokinase activity. In the absence of AMP and fructose-2,6-bisphosphate the dependence of enzyme activity on the concentration of inorganic phosphate is sigmoidal. AMP and fructose-2,6-bisphosphate increase the affinity of phosphofructokinase to inorganic phosphate. At low fructose-6-phosphate concentrations inorganic phosphate amplifies the activating effect of AMP and fructose-2,6-bisphosphate. Yeast phosphofructokinase is more sensitive to ATP inhibition in the absence of inorganic phosphate than in its presence. While in the absence of inorganic phosphate a definite ATP inhibition prevails even at high levels of AMP or fructose-2,6-bisphosphate, the ATP inhibition can be relieved by the cooperation of inorganic phosphate and fructose-2,6-bisphosphate. These effects of inorganic phosphate provide an explanation for the stimulation of glycolysis under anaerobic conditions by inorganic phosphate at unchanged concentrations of AMP and fructose-2,6-bisphosphate (Lagunas and Gancedo, Eur. J. Biochem. 137, 479-483 (1983)).

Adenosine Monophosphate↗
PubMed1985

Glycolytic and gluconeogenic states in an enzyme system reconstituted from phosphofructokinase and fructose 1,6-bisphosphatase.

Transitions between glycolytic and gluconeogenic states have been investigated in an open and homogeneous enzyme system containing phosphofructokinase, fructose 1,6-bisphosphatase, pyruvate kinase, adenylate kinase and glucose 6-phosphate isomerase. The direction of substrate flow was found to depend on the maximum activities of phosphofructokinase and fructose 1,6-bisphosphatase as well as on the influx concentrations of fructose 6-phosphate and fructose 1,6-bisphosphate. At high and low maximum activities of phosphofructokinase and fructose 1,6-bisphosphatase unique and stable stationary states occur, whereas at intermediate enzyme concentrations sustained oscillations emerge. Stationary states with a low rate of substrate cycling demand both appropriate enzyme concentrations and an adequate substrate supply. Accordingly, transitions between efficient glycolytic and gluconeogenic states require changes of the enzyme concentrations and of the supply of substrates. Such transitions exhibit a transient oscillatory response. The sustained oscillations generated at intermediate activities of phosphofructokinase and fructose 1,6-bisphosphatase lead to a significant diminution of the rate of substrate cycling when compared with the respective steady state values. During the oscillations glycolytic and gluconeogenic states are consecutively passed through. Because of this a temporal organization of the antagonistic reactions is achieved. In our system the kinetic organization of the two opposite reactions is mainly brought about by the reciprocal allosteric effects of AMP on the activities of the two enzymes.

Adenosine Triphosphate↗
PubMed1985

Dynamic structures of the fructose 6-phosphate/fructose 1,6-bisphosphate cycle in a reconstituted enzyme system.

The dynamics of the fructose 6-phosphate/fructose 1,6-bisphosphate cycle was investigated in an open and homogeneous system reconstituted from purified enzymes. In addition to phosphofructokinase and fructose 1,6-bisphosphatase, pyruvate kinase, adenylate kinase and glucose 6-phosphate isomerases are involved. The time evolution of the metabolite concentrations is governed by a set of differential equations which take into account flow processes and enzymic conversions of metabolites. Depending on the experimental parameters stable attractors, multiple states and sustained oscillations occur. The main source of the nonlinear dynamics is the reciprocal effect of AMP on the activities of phosphofructokinase and fructose 1,6-bisphosphatase. States are characterized by the net flow rates of substrates and by the rate of futile substrate cycling. For efficient glycolytic states high ratios between the influx rates of fructose 6-phosphate and fructose 1,6-bisphosphate and between the maximum activities of phosphofructokinase and fructose 1,6-bisphosphatase must be maintained, while for an efficient gluconeogenic mode the reverse must hold. Fructose 2,6-bisphosphate exerts reciprocal effects on the activities of phosphofructokinase and fructose 1,6-bisphosphatase. In dependence on the experimental conditions fructose 2,6-bisphosphate was found either to generate or to extinguish oscillations.

Animals↗
PubMed1985

Purification and some properties of lysosomal alpha-glucosidase of rat liver.

Acid alpha-glucosidase was purified from the lysosomal/mitochondrial fraction of rat liver by acid precipitation, ammonium sulphate precipitation and affinity chromatography on Sephadex G 100, resulting in 17000-fold enrichment from that of the liver homogenate. The molecular weight of the enzyme was estimated to be 125000 from analytical gel filtration experiments. On SDS-polyacrylamide gel electrophoresis the purified enzyme showed only a single band having an apparent molecular weight of about 64000. Based on these results, it is concluded that lysosomal liver alpha-glucosidase consists of two subunits. The discontinuous system of SDS-polyacrylamide gel electrophoresis, however, revealed two closely migrating protein bands suggesting heterogeneity of the enzyme subunits.

Ammonium Sulfate↗
PubMed1984

Inhibition of rat liver phosphofructokinase-2 by phosphoenolpyruvate and ADP.

Phosphofructokinase-2 from rat liver is inhibited by phosphoenolpyruvate and ADP. Phosphoenolpyruvate reduces the maximum activity in respect to fructose-6-phosphate and ATP but does not give rise to complete inhibition of phosphofructokinase-2. ADP increases the apparent Michaelis constant of the enzyme for ATP and leaves the maximum activity in respect to ATP unchanged. The apparent Michaelis constant for fructose-6-phosphate is not influenced by ADP.

Adenosine Diphosphate↗
PubMed1984

Inhibition of fructose-1,6-bisphosphatase from pig liver by fructose-6-phosphate.

The inhibition of the neutral form of fructose-1,6-bisphosphatase from pig liver by fructose-6-phosphate was investigated in the substrate concentration range of 0.05-500 microM by determination of the rate of formation of labelled inorganic phosphate from [1-32P]fructose-1,6-bisphosphate. The inhibition of the enzyme by fructose-6-phosphate is biphasic, the extent of inhibition decreases with increasing substrate concentrations. Even at high concentrations of fructose-6-phosphate the enzyme is not inhibited completely. The results were interpreted in terms of the model of MONOD, WYMAN and CHANGEUX [10] by assuming a weak competition of fructose-6-phosphate and fructose-1,6-bisphosphate at the catalytic site and a cooperation of the two ligands at the same allosteric site.

Animals↗
PubMed1984

Interaction of Cibacron blue F3G-A with yeast phosphofructokinase.

The binding of Cibacron blue F3G-A to yeast phosphofructokinase was investigated by means of ultracentrifugation. Four moles of Cibacron blue are tightly bound per subunit of phosphofructokinase (dissociation constant = 0.26 microM). This stoichiometry does not correspond to the stoichiometry of ATP binding to yeast phosphofructokinase (two moles of ATP per subunit). Moreover, 32 moles of the dye are bound per subunit of phosphofructokinase to a second class of binding sites with low affinity (dissociation constant = = 53 microM). The action of Cibacron blue on yeast phosphofructokinase cannot be explained completely in terms of its function as ATP analogue.

Adenosine Triphosphate↗
PubMed1984

Cooperation of fructose-2,6-bisphosphate and AMP in the activation of yeast phosphofructokinase.

Yeast phosphofructokinase is effectively activated by AMP and fructose-2,6-bisphosphate. Both effectors influence the sensitivity of the enzyme with respect to fructose-6-phosphate and increase the respective maximum activities. The dependence of phosphofructokinase activity on the concentration of fructose-2,6-bisphosphate was measured at different AMP concentrations and vice versa. By AMP the half activation constant for fructose-2,6-bisphosphate is decreased by one order of magnitude. The affinity to AMP is significantly increased by fructose-2,6-bisphosphate. AMP increases the maximum activity of the enzyme with respect to fructose-2,6-bisphosphate only slightly, while the maximum activity with respect to AMP is drastically increased by fructose-2,6-bisphosphate. The interaction of the two activators is most pronounced at low levels of fructose-6-phosphate and at high concentrations of ATP.

Adenosine Monophosphate↗
PubMed1984

Influence of inorganic phosphate on the kinetic properties of yeast phosphofructokinase.

Yeast phosphofructokinase is effectively activated by inorganic phosphate. In the absence of other allosteric stimulators, inorganic phosphate increases the maximum activity of the enzyme only. In the presence of the activators AMP and fructose 2,6-bisphosphate inorganic phosphate causes changes in the maximum activity and the enzyme affinity to fructose 6-phosphate. Inorganic phosphate augments the sensitivity of phosphofructokinase to the activators AMP and fructose 2,6-bisphosphate and increases the respective maximum activities. The extent of activation of the enzyme by inorganic phosphate prevails at low levels of fructose 6-phosphate and high ATP concentrations.

Adenosine Monophosphate↗
PubMed1984

Effect of enzyme concentrations on sustained oscillations in the fructose 6-phosphate/fructose 1,6-bisphosphate-cycle.

Sustained oscillations were investigated in an open and homogeneous enzyme system reconstituted from phosphofructokinase, fructose 1,6- biphosphatase , pyruvate kinase, adenylate kinase, and glucose 6-phosphate isomerase. The generation of oscillations if mainly due to antagonistic kinetic effects of AMP on phosphofructokinase and fructose 1,6- biphosphatase under the experimental conditions applied. Sustained oscillations were obtained in a broad range of maximum activities of phosphofructokinase or fructose 1,6- biphosphatase are increased. At low maximum activities of the two enzymes oscillations arise, which form a folded limit cycle, while by increasing concentrations of phosphofructokinase or fructose 1,6-bisphosphatase sustained oscillations are introduced, which are restricted to two dimensions.

Adenylate Kinase↗
PubMed1983

Perinatal changes of fructose 2,6-bisphosphate in the rat liver.

In order to investigate a possible regulatory role of fructose 2,6-bisphosphate in early developmental stages, where profound changes in the carbohydrate metabolism are known to occur, this effector was estimated in fetal and postnatal rat liver. Polyphasic changes of the hepatic fructose 2,6-bisphosphate levels were found, which could be correlated to alterations in the glucose metabolism. A minimum in the hepatic fructose 2,6-bisphosphate level at the -3rd day coincides with the initiation of glycogen synthesis and its increase two hours after birth concurs with glycogen mobilization.

Aging↗
PubMed1983

Biochemistry of liver development in the perinatal period.

Just before birth, changes occur in the metabolic capacities of rat liver so that the animal can adapt to changes in the substrate supply. In utero, glucose is the main energy-generating fuel and the liver metabolism is directed towards glucose degradation. The activities of the rate-limiting enzymes of glycolysis, hexokinase and phosphofructokinase, are high. In preparation for post-natal life, when the continuous glucose supply from the mother is interrupted, very large amounts of glycogen are stored in the late fetal liver. With the intake of the fat-rich and carbohydrate-poor milk diet, the animal develops the ability to synthesize glucose de novo from non-carbohydrate precursors. During suckling, metabolic energy is derived mainly from the beta-oxidation of fatty acids, which in turn is an essential prerequisite for the high rate of gluconeogenesis, by yielding acetyl-CoA for the activation of pyruvate carboxylase and by generating a high NADH/NAD ratio for the shift of the glyceraldehyde 3-phosphate dehydrogenase reaction in the direction of glucose formation.--The developmental adaptation of metabolism and the process of enzymatic differentiation are closely connected with the maturation of the endocrine system and the changes in the concentration of circulating hormones. The neonatal regulation of phosphoenolpyruvate carboxykinase and of tyrosine aminotransferase by variations in the hormonal milieu around birth, and also the interaction of hormonal and nutritional factors in the induction of serine dehydratase and glucokinase at the end of the suckling period, will be discussed in detail.

Amino Acids↗