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D Brox

Publications and source records attributed to D Brox.

16 recordsLinked to original sources
PubMed1995

Fructose 2,6-bisphosphate metabolism in Ehrlich ascites tumour cells.

Cancer cell energy metabolism is characterized by a high glycolytic rate, which is maintained under aerobic conditions. In Ehrlich ascites tumour cells, the concentration of fructose 2,6-bisphosphate (Fru-2,6-P2), the powerful activator of 6-phosphofructo-1-kinase, is tenfold increased. The bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2/FBPase-2), synthesizing and degrading Fru-2,6-P2, was characterized. The molecular mass is 120 kDa. The dependence of PFK-2 activity on the substrate concentrations is hyperbolic (Km for Fru-6-P = 0.09 mM; Km for ATP = 0.7 mM), while the dependence of the FBPase-2 activity on the concentrations of Fru-2,6-P2 is sigmoidal (K0.5 for Fru-2,6-P2 = 4 microM). The PFK-2/FBPase-2 activity ratio is 1. PFK-2 activity is inhibited by citrate (I0.5 = 0.17 mM) and phosphoenolpyruvate (I0.5 = 0.08 mM) but only weakly by glycerol 3-phosphate (I0.5 = 1.57 mM). In contrast to the liver enzyme, the activity of tumour PFK-2/FBPase-2 is not influenced by the action of cAMP-dependent protein kinase. The kinetic properties as well as ion-exchange chromatography pattern differ from their normal counterparts in liver and muscle. The properties are likely to contribute to the maintenance of the high glycolytic rate in these tumour cells.

Alkaline Phosphatase↗
PubMed1987

Membrane skeleton alteration--a factor promoting IgG receptor expression in the erythrocyte membrane.

IgG receptor expression after selective cross-linking of spectrin by means of diamide was investigated. A diamide concentration dependent IgG loading of erythrocytes was observed. Furthermore, diamide causes disturbance of lipid asymmetry, decrease of the anisotropy after topooptical staining of the glycocalyx, increase of the phagocytosis index and aggregation of the IMP's. Our findings support the hypothesis that the arrangement of the membrane skeleton at the inner aspect of the membrane is decisive not only for the lipid asymmetry but also for the spatial structure of the glycocalyx at the outer aspect of the membrane and thus for the degree of exposure and arrangement of IgG-receptors, which are thought to be localized at an extracellular portion of band 3 protein.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1980

[Protein changes of the erythrocyte membrane during blood preservation].

The present study was conducted on erythrocytes banked in ACD-AG medium for 1, 21, or 42 days at 4 degrees C. Erythrocyte membrane proteins were analysed by means of SDS-polyacrylamide gel electrophoresis in relation to the action of beta-mercaptoethanol. Under banking conditions proteins of the erythrocyte membrane formed 380 000--420 000 daltons aggregates, presumably heterodimers of spectrin I and II, and very high molecular weight aggregates (MG > 600 000 daltons). Part of the aggregated proteins were cross-linked by disulfide bridges, which are subject of the reduction by beta-mercaptoethanol. The nonreducible components were considered an irreversible alteration of the erythrocyte membrane. Many samples of banked erythrocytes exhibited an increase of protein band II.3 (MG = 185 000 daltons) and band IV.2 (MG = 72 000 daltons). The amount of protein band VI (GAPDH) was shown to depend on both banking time and conditions of haemolysis. A modified hypotonic haemolysis with an additional intermediate alkaline incubation of ghosts resulted in a considerable decline of protein band VI of banked erythrocytes. Substraterich incubation of banked erythrocytes, which raised the ATP level well above normal, could only partially restore the membrane bound portion of protein band VI.

Blood Preservation↗
PubMed1977

The effects of calcium on glycolysis and ATP concentration in complete and membrane-poor hemolyzates of human erythrocytes.

Hemolyzates prepared from packed human red cells with 30 micrometer total calcium were employed as a means to examine the relationship between ATP consumption and lactate formation. Hemolyzates exposed to ultracentrifugation accumulate membrane fragments in the top layer yielding membrane-poor fractions in the buttom layers of the centrifuge tube. Lactate formation accompanied by ATP depletion amounts to 12 mumoles per ml and hour in complete hemolyzates fortified with NAD. Complexation of calcium results in about 50% inhibition of the lactate formation with a concomitant increase of ATP. Lactate formation is reduced in membrane-poor hemolyzates approximately concurrently to the extent of membrance removal which produces no discernible change in the glyceral-dehydephosphate dehydrogenase activity. 50--200 micrometer total calcium has no effect on the membrane-independent lactate formation which amounts to 1--2 mumoles per ml and hour. Triton X-100 seems to solubilise also the membrane components responsible for the high calcium-dependent ATP consumption which governs the lactate formation.

Adenosine Triphosphate↗
PubMed1975

[Studies on the osmotic resistance and the viability of amidinated erythrocytes].

The present studies are concerned with properties of amidinated erythrocytes. The reactions of dimethyladipimidate with proteins in solution and red blood cells, respectively, result in an intermolecular cross-linking. Following an amidination of human serum albumin or human gamma-globulin cross-linked products of increased molecular weight have been demonstrated by polyacrylamide gel and immune electrophoresis. Human erythrocytes previously amidinated intensely, exhibit a restricted motility of membrane particles and cross-linked hemoglobin. Intensely amidinated erythrocytes are resistant against distilled water, and they do no longer agglutinate. The findings presumably indicate an increased permeability of the amidinated red cell membrane. The glycolytic activity was found to be normal in moderately amidinated erythrocytes. In comparison with normal red blood cells, previously moderately amidinated erythrocytes of the rat become sequestered more quickly after re-injection into the vascular system.

Amidines↗