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Biomedical subjects

M Kretschmer

Publications and source records attributed to M Kretschmer.

32 records · Page 2Linked to original sources
PubMed1989

Investigations on the influence of copper succinate on the production of superoxide anion radicals by bovine small intestinal mucosa cells.

The effect of an experimental ischemia lasting for 45 minutes and a subsequent period of reperfusion of equal length on the activity of xanthine oxidase (XO) and microsomal NADPH-cytochrome P450 reductase (NADPH-CR) were investigated in the small intestinal mucosa of male neonatal calves of the breed German "Schwarzbunte". The activity of the NADPH-CR was determined by chemiluminescence. The activity of XO decreased during ischemia, but rose to values above the control level following reperfusion. 5 mg of Cu2(succinate)2 (CuSu) administered either intraarterially or intraluminally during reperfusion prevented the rise in XO. Formation of malondialdehyde decreased in the presence of CuSu. The NADPH-CR likewise showed subnormal activity values during ischemia, but also remained at a low level during reperfusion. The activity of this enzyme was further lowered by local intraarterial or intraluminal administration of 5 mg of CuSu and by 120 mg of CuSu administered intravenously during the reperfusion. These results are discussed with regard to the superoxide anion radical induced tissue lesions observed during reperfusion.

Animals↗
PubMed1989

Kinetics of 6-phosphofructo-2-kinase from Saccharomyces cerevisiae: inhibition of the enzyme by ATP.

6-Phosphofructo-2-kinase (PFK-2) was purified from yeast and separated from fructose-2,6-biphosphatase (FBPase-2). The purification procedure involved polyethylene glycol fractionation followed by chromatography on DEAE-Sephacel. PFK-2 and FBPase-2 were copurified in these steps. Separation of the two enzymes resulted from Sephacryl S-300 Blue chromatography. Then, PFK-2 was chromatographed on CM-Sephadex and eluted with a gradient of KCl. Finally, PFK-2 was rechromatographed at CM-Sephadex and specifically eluted with fructose 6-phosphate. PFK-2 (specific activity 1.3 U/mg) was purified about 25,000-fold. The enzyme is inhibited by ATP which is particularly pronounced at low concentrations of magnesium and fructose 6-phosphate. Phosphoenolpyruvate and sn-glycerol 3-phosphate are inhibitors of the enzyme.

Adenosine Diphosphate↗
PubMed1989

Regional histochemical aspects of xanthine oxidase activity in ischemic and reperfused small intestine of the rat.

The study describes regional changes of xanthine oxidase and succinate dehydrogenase activities as shown by the ischemic and reperfused small intestine of the rat. The results are obtained with enzyme histochemical methods, including densitometrical verifications, and are substantiated with biochemical enzyme determinations. The decrease of xanthine oxidase activity was best visible in the anoxic duodenum and jejunum, where the findings of histochemical enzyme determinations agreed with those achieved biochemically. The activities of succinate dehydrogenase as measured densitometrically may serve as a further control, considering also the typical intracellular distribution of the reaction products.

Animals↗
PubMed1987

Fructose-2,6-bisphosphatase and 6-phosphofructo-2-kinase are separable in yeast.

Fructose-2,6-bisphosphatase was purified from yeast and separated from 6-phosphofructo-2-kinase and alkaline phosphatase. The enzyme released Pi from the 2-position of fructose 2,6-bisphosphate and formed fructose 6-phosphate in stoichiometric amounts. The enzyme displays hyperbolic kinetics towards fructose 2,6-bisphosphate, with a Km value of 0.3 microM. It is strongly inhibited by fructose 6-phosphate. The inhibition is counteracted by L-glycerol 3-phosphate. Phosphorylation of the enzyme by cyclic-AMP-dependent protein kinase causes inactivation, which is reversible by the action of protein phosphatase 2A.

Chromatography, Affinity↗
PubMed1987

The appearance of a critical input concentration of fructose 6-phosphate in the 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase cycle.

Stationary states of the fructose 6-phosphate/fructose 2,6-bisphosphate cycle were investigated in relation to the input concentration of fructose 6-phosphate. Below a critical input concentration of fructose 6-phosphate very low levels of fructose 2,6-bisphosphate were obtained. Above this point the fructose 2,6-bisphosphate changes in direct proportion to the input of fructose 6-phosphate. Phosphorylation of the enzyme causes an increase of the critical input concentration of fructose 6-phosphate. The control coefficients for fructose 2,6-bisphosphate have their maximum at the critical input concentration of fructose 6-phosphate.

Fructosephosphates↗
PubMed1987

Some aspects of a non-linear effect of zinc ions on the histamine release from rat peritoneal mast cells.

Addition of zinc-chloride or zinc-orotate to the lavage medium successfully influences the histamine release from rat peritoneal mast cells. The effect of these zinc compounds is not doses-linear. 20 and 30 mg/l ZnCl2 cause a rather strong, 0.5, 5 and 10 mg/l ZnCl2 a weak depression in the release of histamine. An increase in the histamine release is caused by 40 mg/l ZnCl2. A similar, likewise non-doses-linear effect, can be observed with zinc-orotate. Concentrations of 10 and 30 mg/l zinc-orotate cause a decrease of the release; 0.05, 0.1, 1 and 60 mg/l have only minimal effects; an addition of 90 mg/l leads to an increase in the histamine release. Related to the Zn2+ ion the effect of zinc-chloride and zinc-orotate is not equivalent.

Animals↗
PubMed1986

Regulation of immunoglobulin production after human marrow grafting. The role of helper and suppressor T cells in acute graft-versus-host disease.

The effect of acute graft-versus host disease (GVHD) on T4 and T8 lymphocyte regulation of in vitro immunoglobulin production was explored. The peripheral blood lymphocytes from 20 patients were studied sequentially in the first 100 days after sibling bone marrow grafting for hematologic malignancy or aplastic anemia. T and non-T lymphocytes were prepared from peripheral blood by Ficoll-Hypaque density gradient centrifugation and sheep erythrocyte rosetting. T cells were enriched for T4 or T8 cells and cocultured for six days with pokeweed mitogen and autologous non-T or T and non-T cells from unrelated normal individuals. Immunoglobulin production was assessed using a reverse hemolytic plaque assay. All three patients without acute GVHD had failure of non-T cells to secrete immunoglobulin, one had failure of helper T cell activity, and 2 developed suppressor T cells. Similarly, all six patients studied sequentially after the development of GVHD had non-T-cell failure, five developed helper T cell failure, and five had suppressor T cells. These data suggest no difference in lymphocyte function before or after the development of acute GVHD. When the T cells of these patients were split into T4 and T8 subpopulations and studied for immunoglobulin production there was helper T cell failure in 4 of 9 tests with enriched T4 populations. Five of 9 tests with T8 enriched populations showed suppressor activity. Suppressor T cell function was also seen in 4 of 9 tests with with T4-enriched populations. These data show that T cell function does not necessarily correlate with the surface phenotype during the first 100 days after grafting. A role for cytomegalovirus (CMV) infection in bringing out suppressor activity is suggested, because among patients without GVHD, 6 of 8 tests in CMV-positive patients showed suppressor cells compared with none of 4 tests in patients without CMV infection.

Antibody Formation↗
PubMed1985

Quasi-stationary concentrations of fructose-2,6-bisphosphate in the phosphofructokinase-2/fructose-2,6-bisphosphatase cycle.

The cooperation of phosphofructokinase-2 and fructose-2,6-bisphosphatase is investigated. Experimentally derived rate laws of the kinase and bisphosphatase activities introduced into the respective differential equations permitted to describe the time evolution of fructose-2,6-bisphosphate to quasi-stationary levels. The two enzyme activities were found to exert strong temperature dependence. The quasi-stationary levels of fructose-2,6-bisphosphate, however, are independent on temperature.

Adenosine Triphosphate↗
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↗