Temperature-dependence of activation and inhibition of rat-brain adenosine triphosphatase activated by sodium and potassium ions

The temperature dependence of activation by phosphatidylserine of the sodium pump adenosine triphosphatase

1. Treatment of rabbit brain homogenates with deoxycholate reduced ouabain-insensitive ATPase sixfold and subsequently adding phosphatidylserine had no effect. Ouabain-sensitive ATPase was made entirely latent but it was fully restored on adding phosphatidylserine.2. Temperature and pH were varied to see if the reconstituted system resembled that in the original membranes. Linear Arrhenius plots were always obtained with the homogenate, and the activation energy was higher for the ouabain-sensitive than for the ouabain-resistant enzyme.3. A break at about 15 degrees C was found in the Arrhenius plot of the reconstituted enzyme, but there was no break without added phosphatidylserine or when ouabain was added. The break suggests that the conformation and catalytic activity of the enzyme protein depended on the physical state of phosphatidylserine.

Permeability of a cell membrane junction. Dependence on energy metabolism

The ion permeability of the membrane junctions between Chironomus salivary gland cells is strongly depressed by treatments that are generally known to inhibit energy metabolism. These treatments include prolonged cooling at 6 degrees -8 degrees C, and exposure to dinitrophenol, cyanide, oligomycin, and N-ethylmaleimide. Intracellular injection of ATP appears to prevent depression of junctional permeability by dinitrophenol or to reverse it. Ouabain, azide, p-chloromercuriphenylsulfonic acid, reserpine, and acetazolamide fail to depress junctional permeability. Thus the ion permeability of the junctional membranes appears to depend on energy provided by oxidative phosphorylation. Possible energy-linked processes for maintaining junctional permeability are discussed, including processes involving transport of permeability-modifying species such as Ca(++).

Physical and chemical reactions of phosphates in red cell membranes in relation to active transport

1. A study has been made of the chemical reactions associated with the active transport of sodium and potassium in human red cells, with special reference to the action of oligomycin and the labelling of cell membranes by radioactive ATP.2. Oligomycin had the same effects as ouabain on the various aspects of active transport in red cells. It inhibited sodium and potassium transport, the transport ATPase, and the lactate production that is controlled by the sodium pump.3. When cell membranes were incubated with radioactive ATP they became labelled. The labelling, however, was unrelated to the activity of the transport ATPase. Incubation of membranes and intact cells showed that the labelling was a result of physical adsorption of inorganic phosphate to the membranes.4. The results show that if there is a phosphate intermediate in the reaction of the transport ATPase in human red cell membranes, then it is present in amounts too small to be detectable by the methods that have been successfully used with organs such as brain and kidney.

Influence of temperature acclimatization on the temperature-dependence and ouabain-sensitizing of goldfish intestinal adenosine triphosphatase

1. Homogenates of goldfish intestinal mucosa were separated into various fractions by differential centrifugation. Both adenosine-triphosphatase and beta-glycerophosphatase activities were found to be concentrated mainly in a membrane fraction which sedimented after 1200000g-min. 2. This membrane adenosine-triphosphatase system was activated by Na(+)+K(+) and inhibited by ouabain. 3. The ouabain-sensitive adenosine-triphosphatase activity was high and the ouabain-insensitive activity low in membrane fractions prepared from fish acclimatized previously to 8 degrees . The opposite was true for fish acclimatized to 30 degrees . 4. The Arrhenius plots of ouabain-sensitive and ouabain-insensitive adenosine-triphosphatase activities, measured from 5 degrees to 30 degrees , showed discontinuities at incubation temperatures that varied with the previous acclimatization temperature of the fish. 5. It is considered that modification of the membrane adenosine-triphosphatase system in goldfish intestinal mucosa may serve to regulate Na(+) transport at different environmental temperatures.

Potassium transport and nucleoside metabolism in human red cells

1. A study has been made of active cation transport in relation to the metabolism of nucleosides and deoxynucleosides in human red blood cells.2. Lactate production from inosine depended on the cellular inorganic phosphate available for phosphorolysis and was raised to some 4 times the normal rate from glucose. Inosine inhibited glucose metabolism according to the amount of glucose-6-phosphate produced. Guanosine behaved similarly, but glucose-6-phosphate was not formed from adenosine, deoxyinosine and deoxyguanosine.3. Glucose metabolism was related to the ATP content of the cells, which was raised by incubation with adenosine, or with inosine plus adenine.4. Adenosine and deoxyadenosine raised the potassium influx above the values found with inosine and deoxyinosine under conditions when the lactate production was constant. Active potassium influx was correlated with the ATP concentration in the cells, but independent of the lactate production when the latter was raised above normal.