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J F Hoffman

Publications and source records attributed to J F Hoffman.

88 records · Page 5Linked to original sources
PubMed1972

Some kinetic and metabolic characteristics of calcium-induced potassium transport in human red cells.

When fresh human erythrocytes or their ghosts are incubated with Ca + IAA (iodoacetic acid) + adenosine, K permeability increases; K permeability also increases when energy-depleted cells or their ghosts are incubated with Ca alone. Na transport decreases or remains unaltered in both situations. The Ca-induced increase in K permeability in the depleted cell system is qualitatively similar to that seen in the fresh cell system and furnishes a means for studying the metabolic dependence of calcium's action. Studies with the depleted system suggest that the normal refractiveness of the cell to calcium is provided by a metabolically dependent substrate. Removal of this substrate allows Ca to enter the cell and exert its effect. By using (47)Ca, a maximum value was obtained (3-7 x 10(-6) moles/liter of red blood cells) for the quantity of calcium that is taken up by the cell and responsible for the change in K permeability. Measurements of the unidirectional fluxes of K, obtained during the time Ca increases K permeability, appear to satisfy the flux ratio equation for passive diffusion through a membrane.

Adenosine↗
PubMed1971

Active cation transport and ouabain binding in high potassium and low potassium red blood cells of sheep.

Red cells from high K sheep contained 82 mM K/liter cells and had a pump flux of 0.86 mM K/liter cells x hr; similarly, LK cells had 16.5 mM K/liter cells and a pump flux of 0.12 mM K/liter cells x hr. Using [(3)H]-ouabain, the relation between the number of ouabain molecules bound per cell and the concomitant per cent inhibition of the pump was found to be approximately linear for both HK and LK cells. The number of glycoside molecules necessary for 100 % inhibition of the pump was 42 for HK cells and 7.6 for LK cells, after correction for six nonspecific binding sites for each type of cell. The ratio of ouabain molecules/cell at 100 % inhibition was 5.5, HK to LK, and the ratio of the normal K pump fluxes was 7.2, HK to LK. The similarity of these ratios suggests that an important difference between HK and LK cells, determining the difference in pump fluxes, is the number of pump sites. The turnover times (ions/site x min) are 6000 and 4800 for HK and LK cells, respectively. The results also indicate a high specificity of binding of ouabain to pump sites.

Animals↗
PubMed1971

Nucleotide requirements for sodium-sodium exchange catalysed by the sodium pump in human red cells.

1. Resealed red cell ghosts containing a variety of nucleoside triphosphates, or a mixture of tri- and diphosphates, were allowed to lose (24)Na into a 10 mM-K medium or a K-free high-Na medium in the presence and absence of ouabain.2. Only ATP supported a ouabain-sensitive Na:K exchange in the 10 mM-K medium, or a ouabain-sensitive Na:Na exchange in the K-free medium.3. Because of ATPase and adenylate kinase activity, it is difficult to control the levels of ATP and ADP inside resealed red cell ghosts. Some control was achieved by incorporating into the ghosts an ATP regenerating system consisting of creatine phosphate and creatine kinase.4. Measurements of (24)Na efflux from ghosts prepared in this way showed that ADP is required for the ouabain-sensitive exchange of Na that occurs in K-free high-Na media, but not for the normal exchange of Na for K that occurs in K-containing media.5. The significance of these findings is discussed.

Adenosine Diphosphate↗
PubMed1970

Partial purification of the ouabain-binding component and of Na,K-ATPase from human red cell membranes.

Ghosts of human red cells were incubated with tritiated ouabain in the presence of ATP, Mg, and Na, conditions under which ouabain binds with high specificity to Na:K transport sites. The labeled membranes were solubilized with sodium dodecyl sulfate and dialyzed. Sodium dodecyl sulfate solubilizes most of the membrane protein and leaves most of the tritiated-ouabain bound to a solubilized component. Solubilized Na,K-ATPase could also be obtained after dialysis. The solubilized membranes were centrifuged in a sucrose density gradient. The ouabain-membrane complex and the Na,K-ATPase sedimented faster than the bulk of the protein. The ouabain-membrane complex and the Na,K-ATPase appeared to be identical and were purified about eightfold relative to the starting material. These results represent a step toward the isolation and characterization of the cation transport mechanism in red cell membranes.

Adenosine Triphosphatases↗
PubMed1967

The role of membrane phosphoglycerate kinase in the control of glycolytic rate by active cation transport in human red blood cells.

When the internal Na of human red cells is raised, both K influx and lactate production increase and become more sensitive to the inhibitory action of ouabain. This occurs with either glucose or purine nucleoside as substrate. Fresh whole hemolysates enriched with Na and Mg will convert intermediates above the triose phosphate dehydrogenase step to lactate at a rate which is slowed by ouabain. Intermediates beyond the phosphoglycerate kinase step (PGK) are metabolized at a very rapid rate which is not affected by ouabain. No metabolic effects of ouabain were found in ghost-free hemolysates. Hemoglobin-free ghosts were shown to have both triose phosphate dehydrogenase and PGK activity. The rate of this two-enzyme sequence was found to be a function of the ADP concentration, being maximal when ADP > 0.35 mM. Initial addition of ATP to the ghost system rendered the forward rate of the sequence sensitive to the inhibitory action of ouabain. When the sequence was run in reverse, no inhibitory effect of ouabain could be demonstrated. It is concluded that membrane PGK is a point at which the Na-K transport system can influence the metabolic rate and that this action is possibly exerted via a compartmentalized form of ADP which is an immediate substrate for the ghost PGK.

Adenine Nucleotides↗