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Biomedical subjects

F Koller

Publications and source records attributed to F Koller.

At least 19 recordsLinked to original sources
PubMed1991

Indium-111-labeled low-density lipoprotein binds with higher affinity to the human liver as compared to iodine-123-low-density-labeled lipoprotein.

The interaction of 111In-low-density lipoprotein (LDL) and 123I-LDL with human liver-plasma membranes was investigated and compared. LDLs were isolated by sequential ultracentrifugation and radiolabeled either with 123I (using lodogen or iodine-monochloride) each followed by purification with gel-chromatography or dialysis) or 111In (using cyclic DTPA-anhydride). LDL concentrations of 0.1 to 32 micrograms protein/ml were used for direct binding assays investigating the specific binding of labeled LDL (in the presence of a 50-fold excess of unlabeled LDL) to human liver apoB-receptors. In separate experiments, displacement of bound 111In-(123I)-LDL by unlabeled LDL was studied. Human liver plasma membranes bound 239 +/- 26 ng protein of 111In-LDL/mg protein and 148 +/- 18 ng protein of 123I-LDL/mg protein specifically (p less than 0.001). The corresponding dissociation constants were 0.6 +/- 0.2 and 1.2 +/- 0.7 micrograms protein/ml, respectively (p less than 0.001). The capacity of unlabeled LDL to displace bound 111In-LDL was four times higher than that for 123I-LDL (IC50: 1.7 +/- 0.7 versus 7.7 +/- 1.0 micrograms protein/ml). No significant differences among the different methods of iodination of LDL were found. The findings show that 111In-labeled lipoproteins might be a better ligand for lipoprotein-receptor binding studies as compared to radioiodinated lipoprotein products.

Adult↗
PubMed1990

myo-inositol oxygenase from rat kidneys. Substrate-dependent oligomerization.

myo-Inositol from rat kidneys, an oligomeric protein with apparent molecular mass of about 270 kDa can be dissociated under mild conditions to structured 16.8-kDa monomers. This dissociation can be reversed at high protein concentrations at room temperature. The corresponding apparent dimerization constant K2app = 1.38 x 10(5) M-1, the corresponding rate constant k2 = 350 s-1.M-1, and the apparent constant for the association of dimers, K4app = 2.7 x 10(6) M-1. Reassociation is significantly enhanced in the presence of the substrate and iron(II) (K2app = 9.8 x 10(5) M-1; K4app = 3.75 x 10(6) M-1, k2 = 1750 s-1.M-1, at 20 mM myo-inositol and 0.5 mM FeSO4). Under these conditions almost 100% of the original enzymatic activity was reconstituted. Monomers, with or without bound ligands, lack catalytic activity, whereas the dimer is likely to be the elementary active enzyme-building unit. The effects of myo-inositol on the dimerization lead to the conclusion that this step is both mediated and facilitated by the substrate.

Animals↗
PubMed1989

Purification and identification of the lipoprotein-binding proteins from human blood platelet membrane.

As reported previously, homologous plasma lipoproteins specifically bind to the plasma membrane of human blood platelets. The two major lipoprotein-binding membrane glycoproteins were purified to apparent homogeneity and identified by their mobilities in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, both in the nonreduced and reduced state, by specific antibodies against glycoproteins IIb (GPIIb) and IIIa (GPIIIa), respectively, including the alloantibody anti-PlA1 and monoclonal antibodies. Furthermore, lipoprotein binding to intact platelets is also inhibited in a dose-dependent fashion by preincubation of the platelets with antibodies against these glycoproteins. From these experiments it can be concluded that lipoproteins bind to both components of the glycoprotein IIb-IIIa complex in isolated membranes and intact platelets. High density lipoprotein and low density lipoprotein bind to GPIIIa blotted to nitrocellulose in a way that binding of one species interferes with the binding of the other. Addition of fibrinogen significantly inhibits this binding. The specific binding of fibrinogen to GPIIIa is strongly inhibited in the presence of either of the two lipoproteins. LDL and HDL are specifically bound by isolated GPIIb, too. In our blotting experiments fibrinogen shows no binding to this membrane glycoprotein. On the other hand, fibrinogen significantly interferes with the interaction between GPIIb and the lipoproteins.

Antibodies, Monoclonal↗
PubMed1982

Specific binding sites on human blood platelets for plasma lipoproteins.

Scatchard analysis of the binding of homologous plasma low density lipoproteins (LDL) to human blood platelets shows the existence of a uniform class of saturable specific binding sites. Platelets from healthy donors bound 1470 +/- 640 molecules of LDL per platelet, the constant of association Ka = (6.2 +/- 2.2) X 10-7 l x mol-1. Binding kinetics, temperature dependence, and experiments with formaldehyde-fixed platelets showed that internalization of LDL (at least the labelled apoprotein moiety) did not occur to any considerable degree under the experimental conditions employed. Both very low density lipoproteins (VLDL) and high density lipoproteins 3 (HDL3) markedly inhibited the binding of LDL. In contrast to LDL, HDL3 bound to 3200 +/- 410 binding sites per platelet with a Ka = (9 +/- 1.7) X 10(7) l x mol-1. Additionally, the results of inhibition experiments using both LDL and HDL3 in combination gave evidence, that the sites for HDL3 binding were not identical with those for LDL binding and each inhibited binding of the other noncompetitively with reduction of the binding affinity and the number of available binding sites. VLDL bound to the platelet plasma membrane in a nonspecific-nonsaturable way. Possible significances of the presence of specific LDL receptors on the platelet plasma membrane for recognized functions of these blood elements are discussed.

Binding, Competitive↗
PubMed1979

myo-Inositol oxygenase from rat kidneys. I: Purification by affinity chromatography; physical and catalytic properties.

Using the technique of affinity chromatography on a myo-inositol-substituted Sepharose, the myo-inositol oxygenase from rat kidneys was purified to homogeneity. The active enzyme contains iron, most probably in its divalent form. Electrophoresis on polyacrylamide gel containing sodium dodecylsulphate causes the cleavage of the enzyme protein into apparently identical subunits with a molecular weight of approximately 17,000. The smallest active unit consists of 4 subunits, and is in a pH-dependent equilibium with species consisting of 8, 12, and 16 subunits, respectively, which all show the same specific enzyme activity. In the presence of oxygen the enzyme is highly unstable; at the early stages of inactivation it can be reactivated by reducing agents like NaBH4. Under anaerobic conditions or under the influence of Fe2-chelating agents, the enzyme is also inactivated; this inactivation is caused by the loss of iron and concomitant cleavage into the subunits. It can be reversed by incubation with FeSO4 in the presence of air. If myo-inositol and FeSO4 are present, the reactivation involves an oligomerization to the species with 16 subunits with the uptake of 8 gram-atoms of iron per mole of this species. The enzyme reaction follows Michaelis-Menten kinetics; the Michaelis constants are 4.5 x 10(-2)M for myo-inositol and 9.5 x 10(-6)M for oxygen.

Animals↗
PubMed1977

[Lipoprotein analysis by means of the fluorescence probe 8-anilino-1-naphthalene sulphonic acid (author's transl)].

Single and mixed lipoprotein fractions were successfully analyzed by utilizing the fluorescent propertby of the applied reagent, 8-anilino-naphthalene sulphonic acid. The described method is especially useful for determination of lipoproteins present in high dilution, as found in chromatographic column effluents. The concentration dependence of the developed fluorescence was determined and this served as basis for quantitation. Furthermore, the measured activation spectra show two peaks for each lipoprotein class, the relative intesities being different for each class. The intensity quotient shows a tendency towards linear concentration dependence. Investigation of binary and ternary mixtures showed that the ratio of the two maximum intensities is additive, in contrast to the intensities themselves.

Humans↗
PubMed1976

[The importance of clinical observations for medical research].

Medical progress owes a great deal to the fundamental medical sciences and to the application of chemistry, physics and mathematics to medical problems. However, clinical observations and investigations are still of decisive importance in any field of medicine. By a feed-back mechanism they may even stimulate and fertilize fundamental medical sciences. Thus, our knowledge of the blood coagulation mechanism has been considerably enlarged by clinical analysis of hereditary bleeding disorders. - Chemotherapy of neoplastic diseases started from clinical observations during World War I (production of leucopenia by sulfur mustard gas). - Surgical procedures and their consequences have contributed greatly to our knowledge of thyroid function, of the segmental anatomy of the lung, and of the conduction system of the heart. - Observations of side effects of drugs have often enlarged or completely changed their primary clinical indications: from antibacterial sulfonamides, anti-diabetic, antihypertensive and powerful diuretic drugs have been developed, and from histaminics the modern neuroleptics and antidepressants. - Fundamental immunology has been enormously activated by clinical transplantation of kidney and bone marrow. Selective immunological defects in men, real experiments of nature, contributed much to our knowledge of the various types of allergic response. The quality of clinical investigations, particularly of controlled clinical trials, has been considerably improved during the last two decades. Although it is an applied science the reliability of its results is to-day comparable with that of "pure" natural sciences. However, medicine is more than a natural science: examples of outstanding scientists who at the same time were great and human physicians are presented.

Adrenal Cortex Hormones↗
PubMed1976

[Studies on the heredity and pathogenesis of familial combined hyperlipidemia ("multiple lipoprotein type" hyperlipidemia)].

A family with familial combined hyperlipidemia (multiple-lipoprotein type hyperlipidemia) was investigated with regard to mode of inheritance, phenotypic expression, presence of genetic markers, and biochemical parameters related to lipid metabolism. The family of 22 subjects (13 males, 9 females) was composed of 5 type IIa, 8 type IIb, 1 type IV hyperlipoproteinemias and 5 normolipidemics. The distribution of serum cholesterol and serum triglyceride concentration was bimodal. No relationship was observed between hyperlipidemia and blood groups or histocompatibility antigens. Subjects with high HLA 8 or W 15 had, on the average, higher lipid levels than others. However, these antigens were observed in normolipidemics too. The response to therapy with alufibrate (2g/day) was not uniform. Subjects with marked triglyceride lowering exhibited only moderate cholesterol lowering, and marked cholesterol lowering was associated with poor triglyceride lowering. The reduction in serum lipids was observed in unaffected family members as well. It is therefore concluded that alufibrate does not exert an effect on the defect in familial combined hyperlipidemia but on some unspecific sites probably on lipoprotein lipase. The familial combined hyperlipidemia appears to be transmitted in an autosomal dominant mode and very probably determined by more than one gene.

Adolescent↗
PubMed1976

Myo-inositol oxygenase from oat seedlings.

Enzyme preparations from oat seedlings showing the activity of myo-inositol oxygenase (E.C.1.13.99.1) have been described previously. In contrast to myo-inositol oxygenase preparations from other sources, e.g. rat kidney or yeast, the oat enzyme seemed to exhibit a somewhat less stringent activity, acting on other inositols and inositol methyl ethers as well as on myo-inositol. By purification of the enzyme present in the extract from oat seedlings with the help of an affinity gel specific for enzymes acting on myo-inositol a homogeneous enzyme preparation was obtained, which shows the same strict specificity as the myo-inositol oxygenase from other sources. It has a molecular weight of 62,000 and tends to aggregate to oligomers (up to tetramers) under physiological pH-values; in more alkaline media dissociation to monomers is observed. The action on the other inositols and inositol methyl ethers is apparently due to one or more other enzymes, which are also adsorbed on the affinity gel, but can be separated from the myo-inositol oxygenase by elution with increasing concentrations of myo-inositol.

Edible Grain↗
PubMed1976

Studies on the biosynthesis of cyclitols, XXXIV[l] Purification of myo-inositol 3-methyltransferase from Pisum sativum and of myo-inositol 1-methyltransferase from Vinca minor to homogeneity by affinity chromatography.

With the help of affinity chromatography on an agarose gel containing epi-inositol as the group exhibiting affinity towards enzymes acting on myo-inositol, the two methyltransferases from higher plant materials transforming myo-inositol to D-bornesitol and L-bornesitol, respectively, were purified to homogeneity. The two enzymes show certain similarities as far as pH optima, isoelectric points and specific activities are concerned, but differ significantly in the molecular weight and in their affinity towards the methyl donor, S-adenosyl-L-methionine.

Chromatography, Affinity↗