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Biomedical subjects

W Schoner

Publications and source records attributed to W Schoner.

At least 109 records · Page 6Linked to original sources
PubMed1977

Purification and properties of the pyruvate kinase isoenzymes type L and M2 from chicken liver.

A procedure for the simultaneous purification of both isoenzymes of pyruvate kinase (type M2 and L) from chicken liver has been worked out. Each isoenzyme produces a single band in dodecylsulfate gel electrophoresis. Each has a molecular weight of 190 000 and contains four apparently identical subunits of Mr = 50 000. The isoenzymes differ in their isoelectric points (type L: 6.3; type M2: 8.3) and their kinetic behaviour. Pyruvate kinase type L had an S-shaped phosphoenolpyruvate saturation curve (K 0.5=0.79 mM) which was transformed into an hyperbola in the presence of fructose 1,6-bisphosphate, while type M2 had a phosphoenolpyruvate saturation curve of the Michaelis-Menten type (K0.5=0.2mM). Antibodies against pyruvate kinase type L from chicken liver inactivated type L from rat and partially inactivated type M2 from chicken and rat; but the antibodies against type L did not react with type M1 from chicken breast muscle. It is therefore concluded that, contrary to a previous report (Strandholm, J.J. et al. (1975) Biochemistry 14, 2242-2246), avian liver contains pyruvate kinases type M2 and L as the mammalian liver does.

Adenosine Diphosphate↗
PubMed1977

Inactivation of pyruvate kinase type M2 from chicken liver by phosphorylation, catalyzed by a cAMP-independent protein kinase.

A cAMP-independent protein kinase from chicken liver phosphorylated and inactivated pyruvate kinase type M2 from the same tissue. Complete inactivation was reached when 4 mol of phosphate were incorporated/mol of tetrameric pyruvate kinase. The protein kinase bound with high affinity to pyruvate kinase type M2 (Km value for pyruvate kinase = 6 X 10(-10)M; it phosphorylated phosvitin and casein but not histones, ATP and GTP were substrates. The differences between the properties of this protein kinase in the interconversion of pyruvate kinase and that described previously are discussed.

Animals↗
PubMed1976

The cardiac glycoside receptor: its properties and its correlation to nucleotide binding sites, phosphointermediate, and (Na++K+)-ATPase activity.

Binding of ouabain to its receptor is followed by a directly proportional inhibition of (Na++K+)-ATPase. The stoichiometry of nucleotide binding site, phosphate acceptor site, ouabain binding site in (Na++K+)-ATPase is 1:1:1. Inactivation of (Na++K+)-ATPase by S-[2,4-Dinitrophenyl]-6-mercaptopurine riboside-5'-triphosphate, which probably forms a thioether derivative of ATP with the enzyme, results in the appearance of a low affinity binding site. It is concluded that the covalently bound ATP fixes the enzyme in a E1 conformational state which is characterized by a low affinity for ouabain.

Adenosine Diphosphate↗
PubMed1975

Disulfide of thionosine triphosphate, an ATP-analog inactivating (Na+ + K+)-ATPase.

(Na+ + K+)-activated ATPase in beef brain microsomes is inactivated by the disulfide of thionosine tri[gamma-32P]phosphate, an ATP analog. The inactivation of the enzyme, which is accompanied by an incorporation of radioactivity into the membrane protein, is abolished by ATP or dithiothreitol. Since dithiothreitol restores the activity of (Na+ + K+)-ATPase, which had previously been inactivated by this ATP analog, it is concluded that thionosine triphosphate disulfide reacts with a sulfhydryl group in the ATP binding site of (Na+ + K+)-activated ATPase.

Adenosine Triphosphatases↗
PubMed1975

Stimulation of renal gluconeogenesis by L-alanine and AIB.

L-alanine as well as AIB have been shown to stimulate gluconeogenesis in isolated kidney cortex tubules in a catalytic way. The data reported are consistent with the view, that the stimulation of renal gluconeogenesis by L-alanine and AIB is due to an inhibition of glycolysis at the level of the pyruvate kinase reaction. In the light of results of Carminatti et al. [8], showing that in kidney cortex 70-80% of total pyruvate kinase activity is represented by a type which is insensitive to inhibition by ATP but sensitive to inhibition by alanine, it appears conceivable also from our results, that alanine counteracted by FDP might contribute to the regulation of pyruvate kinase acti-ity and consequently thereby gluconeogenesis in kidney cortex.

Alanine↗
PubMed1975

Cardiac glycoside receptor in potassium depletion.

Ouabain binding capacity of cell membranes is directly related to (Na+ + K+)-ATPase activity. The extent of ouabain inhibition of (Na+ + K+)-ATPase is a measure of ouabain receptor sites occupied. Dissociation constants of the ouabain-receptor complexes are identical in all organs in a single species but vary among different species. K+ decreases the association rate constant of the ouabain receptor interaction without altering the dissociation rate constants. Titration of digoxin-inhibited (Na+ + K+)-ATPase from guinea pig heart with digoxin antibodies shows a reversal of the inhibition at lower antibody concentrations in the presence of K+ than in the absence of K+. It is concluded that digitalis intolerance in acute hypokalemia reflects the increased affinity of the cardiac glycoside receptor under these conditions.

Adenosine Triphosphatases↗