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Biomedical subjects

J Kyte

Publications and source records attributed to J Kyte.

30 records · Page 2Linked to original sources
PubMed1979

Human erythrocyte calmodulin. Further chemical characterization and the site of its interaction with the membrane.

Human erythrocyte and bovine brain calmodulins were indistinguishable by tryptic peptide mapping, indicating that the primary sequence of the two proteins is either very similar or identical. Calcium binding determinations of human erythrocyte calmodulin, by equilibrium dialysis and fluorescence titration, were in close agreement with previous studies on other calmodulins. The calcium-activated adenosine triphosphatase which is stimulated by calmodulin was shown to be firmly associated with smooth erythrocyte plasma membranes devoid of spectrin and actin. Kinetic titration demonstrated that there are 4500 calmodulin binding sites per erythrocyte and that the turnover number of this calcium-activated adenosine triphosphatase is 3000 mumol of Pi . (mumol of site)-1 . min-1 which is similar to the turnover numbers of other transport adenosine triphosphatases. Furthermore, calmodulin stimulates calcium-activated adenosine triphosphatase by a simple enzyme-ligand association.

Animals↗
PubMed1976

Immunoferritin determination of the distribution of (Na+ + K+) ATPase over the plasma membranes of renal convoluted tubules. I. Distal segment.

The distribution of (Na+ + K+) ATPase over the plasma membranes of distal convoluted tubules from canine kidney has been determined. This enzyme is responsible for the coupled active transport of Na+ and K+ across animal cell membranes. Ultrathin frozen sections were cut from fragments of renal cortex and specifically stained with antibodies, which recognize antigenic sites on the enzyme, and ferritin-conjugated goat antirabbit gamma-globulins. It is demonstrated that (Na+ + K+) ATPase is distributed uniformly and at high concentration over the plasma membranes which form the intercellular spaces of this epithelium. The enzyme is located on the luminal surface of the tubules as well but at a much lower concentration. These results, in combination with those of previous determinations of the cation fluxes across this epithelium, can be used to formulate a complete description of the cation movements through this tissue.

Adenosine Triphosphatases↗
PubMed1976

Immunoferritin determination of the distribution of (Na+ + K+) ATPase over the plasma membranes of renal convoluted tubules. II. Proximal segment.

The distribution of (Na+ + K+) ATPase over the plasma membranes of the proximal convoluted tubule from canine renal cortex has been determined. Ultrathin frozen sections of this tissue were stained with rabbit antibodies to this enzyme and ferritin-conjugated goat antirabbit gamma-globulin. It is demonstrated that high concentrations of this enzyme uniformly line the intercellular spaces of this epithelium. The consequences of this observation are discussed in terms of the low resistant tight junctions of these tubules and the isotonic fluid transport which they support. Furthermore, antibodies to (Na+ + K+) ATPase recognize an antigen on the luminal surfaces of the tubules within the brush border. It is proposed that the enzyme is present in this region of the plasma membrane as well, although at much lower concentration. To further substantiate this conclusion, a brush border fraction has been purified from rabbit kidney and been shown to contain significant (Na+ + K+) ATPase. These results contradict earlier conclusions about the location of (Na+ + K+) ATPase in this tissue.

Adenosine Triphosphatases↗
PubMed1975

Structural studies of sodium and potassium ion-activated adenosine triphosphatase. The relationship between molecular structure and the mechanism of active transport.

Sodium and potassium ion-activated adenosine triphosphatase is the enzyme responsible for the active transport of sodium and potassium across the plasma membrane. Strophanthidin, from the external surface of the membrane, and an antibody, from the cytoplasmic surface, bind simultaneously to the large polypeptide subunit of the enzyme. These results demonstrate that this polypeptide chain must span the plasma membrane, having different surfaces exposed on each side. When (Na+ + K+)-ATPase is incubated in the presence of cupric phenanthroline, a reagent which catalyzes the oxidation of cysteine residues to form intermolecular and intramolecular disulfide bonds, a covalent dimer of the larger chains is formed. Several characteristics of this dimerization reaction are consistent with the proposal that at least a noncovalent dimer of large chains exists in the native enzyme. These conclusions are discussed in the context of a specific description for the molecular mechanism of active transport.

Adenosine Triphosphatases↗
PubMed1974

Photoaffinity labeling of the ouabain-binding site on (Na+ plus K+) adenosinetriphosphatase.

An ethyl diazomalonyl derivative of cymarin was synthesized in order to photoaffinity label the cardiac glycoside-binding site on (Na(+) + K(+)) adenosinetriphosphate (EC 3.6.1.3). When a noncovalent complex of the enzyme and this cardiac glycoside derivative was photolyzed, a covalent bond was formed between the ligand and the larger of the two polypeptide subunits of the enzyme. Several control experiments demonstrate that this photochemical reaction occured while the ligand was bound to the site at which it inhibits the enzyme activity. Another specific inhibitor, tentatively identified as the ethyl chloromalonyl derivative of cymarin, produced similar photoaffinity labeling of the larger subunit, demonstrating that the photolytic dissociation of the diazo group may not be responsible for the photochemical reaction. Since the cardiac glycoside-binding site, which is accessible from the outside surface of the plasma membrane, and the phosphorylation site, which is accessible from the inside surface, are both on the larger polypeptide subunit of (Na(+) + K(+)) adenosinetriphosphatase, this polypeptide has sequences exposed to both sides of the membrane.

Adenosine Triphosphatases↗