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Biomedical subjects

E Hofmann

Publications and source records attributed to E Hofmann.

At least 199 records · Page 11Linked to original sources
PubMed1983

Sustained oscillations in a reconstituted enzyme system containing phosphofructokinase and fructose 1,6-bisphosphatase.

In a reconstituted open and homogeneous enzyme system containing phosphofructokinase, fructose 1,6-bisphosphatase, pyruvate kinase, adenylate kinase, and glucose-6-phosphate isomerase sustained oscillations could experimentally be generated. The approach is based on a stirred flow-through reaction chamber. The periodic motions of the reactants are mainly caused by the antagonistic allosteric effects of the adenine nucleotides on the activities of the phosphofructokinase and fructose 1,6-bisphosphatase.

Allosteric Regulation↗
PubMed1983

Similarity of activation of yeast phosphofructokinase by AMP and fructose-2,6-bisphosphate.

Phosphofructokinase from yeast is effectively activated by AMP and fructose-2,6-bisphosphate by increasing the affinity of the enzyme to fructose-6-phosphate and the maximum activity toward this substrate. The enzyme is activated by AMP and fructose-2, 6-bisphosphate both at high and at low concentrations of ATP. The half maximum stimulation concentrations of AMP and fructose-2, 6-bisphosphate are about 200 microM and 2 microM, respectively. At saturating concentrations of AMP and fructose-2, 6-bisphosphate similar maximum activities were observed in the dependence of enzyme activity on the concentrations of fructose-6-phosphate. The fructose-6-phosphate affinity is more enhanced by fructose-2, 6-bisphosphate than by AMP.

Adenosine Monophosphate↗
PubMed1983

Is the solitary kidney a privileged kidney?

In rabbits the renal function of solitary kidneys subjected to ischaemic damage was compared with that of kidneys damaged identically in the presence of a normal contralateral organ. In spite of compensatory hypertrophy of the solitary kidney, no improvement in its tolerance to ischaemia was observed. The solitary kidney is thus not a privileged kidney.

Animals↗
PubMed1983

Diminution of stationary enzyme activities at increases of pyruvate kinase concentration in a reconstituted enzyme system.

In a homogeneous and open enzyme system containing phosphofructokinase, pyruvate kinase, adenylate kinase, and glucose 6-phosphate isomerase the consequences of variations of the enzyme concentrations on the stationary enzyme activities have been investigated. An unexpected behavior was observed upon variation of the maximum activity of pyruvate kinase. Depending on the experimental conditions an increase of the concentration of pyruvate kinase resulted either in a diminution or in a stimulation of the stationary activity of this enzyme. An increase of the maximum activity of phosphofructokinase, however, stimulates both the activities of phosphofructokinase and pyruvate kinase. The experimental results are interpreted in terms of a mathematical model, based on the kinetic properties of the enzymes involved. The correlation between the observed changes of the activities of phosphofructokinase and pyruvate kinase and the appearance of multiple stationary states is discussed.

Adenylate Kinase↗
PubMed1983

Modification of yeast phosphofructokinase with pyridoxal 5'-phosphate.

Modification of yeast phosphofructokinase (E.C. 2.7.1.11) with pyridoxal 5'-phosphate leads to a decreased enzyme activity. ATP at higher concentrations protects the enzyme against inactivation, while fructose 6-phosphate has no effect. At relatively low concentrations of pyridoxal phosphate the inhibition of activity by ATP was decreased or even abolished. AMP still activates the modified enzyme pointing to a separate binding site in the regulatory centre. The dissociation of the phosphopyridoxyl enzyme in products with apparent sedimentation coefficients of about 4-6 S gives evidence that lysine might be involved in the stabilization of the quaternary structure of yeast phosphofructokinase. The incorporation of pyridoxal phosphate in the 17 S form of yeast phosphofructokinase as obtained by a partial proteolysis does not show differences from the 20 S, proteolytically unmodified enzyme.

Electrophoresis↗
PubMed1983

Oscillations in the phosphofructokinase-fructose 1,6-bisphosphatase cycle. I. Purification and kinetic characterization of fructose 1,6-bisphosphatase from pig liver.

A rapid and effective purification procedure for pig liver fructose 1,6-bisphosphatase in neutral form is described. The procedure involves heat treatment and chromatography with CM-Sephadex with specific elution of the enzyme by fructose 1,6-bisphosphate and AMP. The enzyme was found suitable for integration into a reconstituted enzyme system in which the generation of oscillations is investigated. The kinetic properties of fructose 1,6-bisphosphatase are studied under conditions compatible to those applied for the investigation of the dynamic behaviour of the reconstituted system (pH 6.6, presence of inorganic phosphate). The enzyme is significantly inhibited by AMP and fructose 6-phosphate. The substrate fructose 1,6-bis phosphate has a high affinity to the enzyme and was found weakly inhibiting even at high concentrations. The kinetic results are interpreted in terms of a mathematical model which reflects the interaction of the various effectors with the enzyme.

Animals↗
PubMed1983

Oscillations in the phosphofructokinase--fructose 1,6-bisphosphatase cycle. II. Influence of fructose 1,6-bisphosphatase on the character of oscillatory states.

The dynamic behaviour of an open futile cycle composed of phosphofructokinase and fructose 1,6-bisphosphatase has been investigated in a homogeneous reconstituted enzyme system in which the two enzymes cooperate with pyruvate kinase, adenylate kinase and glucose 6-phosphate isomerase. By the kinetic cooperation of phosphofructokinase and fructose 1,6-bisphosphatase various types of dynamic patterns can be generated. In the absence of fructose 1,6-bisphosphatase oscillations do not occur. As experimentally demonstrated, in a definite region of maximum activities of fructose 1,6-bisphosphatase sustained oscillations originate while at higher concentrations of the enzyme damped oscillations appear. At increasing concentrations of fructose 1,6-bisphosphatase damping is strengthened. Finally, at very high concentrations of fructose 1,6-bisphosphatase the metabolites relax monotonously to the stationary states. The observed oscillatory phenomena are mainly caused by the antagonistic effects of AMP on the kinetics of phosphofructokinase and fructose 1,6-bisphosphatase.

Adenylate Kinase↗
PubMed1983

Developmental changes of glycogen phosphorylase b isozymes in rat tissues.

The isozyme distribution of glycogen phosphorylase b was studied in various fetal, neonatal, and adult rat tissues by means of discontinuous polyacrylamide gel electrophoresis in the presence of glycogen in the separating gel. The brain-type isozyme BB being the predominant form in fetal rat tissues is replaced during maturation either partially (brain and kidney) or completely (skeletal muscle and liver) by the isozymes MM or LL, respectively. In the various organs, the developmental formation of the adult phosphorylase isozyme pattern does not proceed simultaneously. The definitive isozyme pattern is expressed in heart muscle at the 19th day of gestation. The isozyme transitions in liver and skeletal muscle are finished about two days after birth, while at this time in the brain just the muscle-type subunit M appears and forms the hybrid MB. The isozyme distribution of the maturated rat brain (BB, MB, MM) is not expressed before the 9th day of postnatal life.

Aging↗
PubMed1983

[Severe neonatal anemia associated with fetomaternal transfusion and persistent fetal circulation].

A newborn infant with massive fetomaternal hemorrhage is reported. The fetal blood loss led to severe late decelerations in the antepartal CTG. The newborn showed a marked anemia (Hb 4.9 g%!) and a rapidly progressive heart failure. Despite blood transfusions and digoxin therapy the infant developed the symptoms of a "persistent fetal circulation". This mechanism may have been responsible for the lethal outcome in other reported cases. A successful therapeutic approach adaptable to the different stages of severity of this dangerous perinatal condition is outlined.

Acute Disease↗
PubMed1982

[The neuroendocrine Merkel cell carcinoma of the skin].

Seven primary skin tumors from 5 women and 2 men were analyzed by light and electron microscopy and immunocytochemistry. The tumors were localized on the face (3 tumors) and on the extremities. The maximum diameter was between 1 and 3.5 cm. Two tumors metastasized to the regional lymph nodes 4 months after excision of the primary, 1 tumor metastasize to the regional lymph nodes after 5 years and the patient died of multiple metastases 8 years after excision of the primary on the forearm. No local recurrences developed. The tumors occurred in the dermis with frequent infiltration of the subcutaneous tissue. The epidermis was intact. The tumor cells formed large solid clusters, while their cytoplasm was faintly basophilic and formed a small rim round the large pale nucleus. In electron microscopy many cells displayed cytoplasmic electron-dense secretory granules with a mean diameter of approx. 100 nm. Immunocytochemistry showed that a large number of cells in all tumors contained neuron specific enolase and many cells of 4 tumors yielded formaldehyde-induced fluorescence. The tumors are therefore of neuroendocrine origin and may derive from merkel cells. They frequently give rise to erroneous diagnosis of metastasis of carcinoma or malignant lymphoma to the skin.

Aged↗
PubMed1982

Transitions between alternate ATP-producing and ATP-consuming stationary states in a reconstituted enzyme system containing phosphofructokinase.

The kinetic behavior of a reconstituted eyzyme system containing purified phosphofructokinase, pyruvate kinase, adenylate kinase, and glucose 6-phosphate isomerase was investigated. Experimentally the approach is based on a stirred flow-through reactor containing gel entrapped enzymes. The experiments were performed on the basis of a mathematical model developed from the kinetic properties of the individual enzymes involved. The system is able to exhibit alternative stable stationary states for one set of experimental conditions (bistability) originating mainly from the allosteric character of the phosphofructokinase. From a functional point of view, these states are either ATP-generating or ATP-consuming. Theoretically, the appearance of alternate steady states gives rise to hysteretic behavior of the system. In fact, transitions between alternate ATP generating stationary states as well as between ATP-generating and ATP-consuming steady states were observed experimentally.

Adenosine Triphosphate↗
PubMed1982

A new procedure for the purification of proteinase B from baker's yeast and interaction of the purified enzyme with a specific inhibitor.

Proteinase B from baker's yeast was purified to homogeneity by applying affinity chromatography with D,L-tyrosine ethyl ester as ligand. The molecular parameters of the product are similar to those reported formerly by other groups. A different form of proteinase B is isolated if affinity chromatography is replaced by CM-cellulose chromatography and gel filtration. In this case a peptide tightly associated with the enzyme was found to occur. This could be identified as an inhibitor fragment produced by limited proteolysis of a proteinase B bound inhibitor induced by proteinase A.

Chromatography, Affinity↗
PubMed1981

Self-stabilization of the energy charge in a reconstituted enzyme system containing phosphofructokinase.

The self-stabilization of the energy charge and of ATP was investigated in an open reconstituted enzyme system containing phosphofructokinase, pyruvate kinase, adenylate kinase, and glucose-6-phosphate isomerase. The experiments were performed in a stirred flow-through reactor containing gel-entrapped enzymes. The dynamics of the system were analyzed theoretically by a model based on the kinetic properties of the individual enzymes. The energy charge was identified as one of the essential variables of the system. According to the theoretical prediction, homoeostasis of the energy charge was observed experimentally when either the maximal activity of phosphofructokinase, the energy charge of the influx solution of the flow rate through the reaction chamber was varied. It is shown that the efficiency of stabilization of the energy charge is related to the occurrence of alternative stationary states.

Adenylate Kinase↗
PubMed1981

External factors limiting the multiplication potential of Tetrahymena.

By variation of nutritional and other external conditions we have determined the factors that limit the multiplication rate and the culture growth in Tetrahymena thermophila. The enriched synthetic medium of Kidder & Dewey (1951), a culture temperature of 29 degrees C, and aeration by agitation were chosen as reference conditions. The final cell density is increased by and proportional to the amount of the complete set of nutrients. Testing single nutritional factors or groups of them revealed that only nitrogen sources yield higher cell densities. But none of them or any combination is as capable of increasing the cell density as the complete medium. Therefore, the medium has to be considered as well balanced. Ammonia, cell density, O2 supply, and pH have been excluded as factors limiting the capacity for multiplication. There are no known factors promoting or inhibiting culture growth.

Ammonia↗