The relationship of the K+-activated phosphatase to the Na+,K+-ATPase

Na,K-dependent adenosine triphosphate phosphohydrolase: activation of the phosphatase reaction by ATP analogs

The effect of N1-substituted analogs of ATP on the hydrolysis of umbelliferone phosphate by Na,K-ATPase has demonstrated: analogs having a negatively charged substituent (N1-oxy- or N1-carbo-methoxy-ATP) and capable of accepting H+ induce an activation similar to that of ATP; N1-methoxy-ATP, containing an uncharged substituent, does not affect the phosphatase reaction at low concentration and inhibits it at higher concentration. It has been assumed that ATP binding to Na,K-ATPase induces formation of a hydrogen bond between the nitrogen atom at the first position of the purine base and appropriate amino acid of active centre, with a subsequent attachment of H+ to ATP, thus facilitating the transition of Na,K-ATPase from the K+- to the Na+-form.

Rat brain (Na+-K+)ATPase: modulation of its ouabain-sensitive K+-PNPPase activity by thimerosal

1. The (Na+ + K+) ATPase activity of a rat brain synaptic membrane preparation was inhibited by 10(-5) M thimerosal. 2. The ouabain inhibitable K+-PNPPase activity of thimerosal treated membranes was compared with that of untreated membranes with respect to sensitivity to temperature, ouabain, K+ and ATP. 3. All those kinetic characteristics were substantially altered by treatment with thimerosal.

Adenosine triphosphatase localization in the branchial heart of Sepia officinalis L. (Cephalopoda)

Sodium- and potassium-dependent adenosine triphosphatase (Na+--K+-ATPase) is demonstrated in the branchial heart of Sepia officinalis L. by biochemical, cytochemical and autoradiographical methods. The biochemical data indicate the presence of Na+--K+-ATPase, shown by potassium and magnesium dependency and inhibition by ouabain. Cytochemically and autoradiographically, the enzyme is localized in the sarcolemma of the muscle cells. The positive reaction of the transparent cells (type I cells) is due to activity of alkaline phosphatases. The dark cells (type II cells) react negatively. In addition to the Na+--K+-ATPase, a magnesium-activated adenosine triphosphatase (Mg2+-ATPase) and a bicarbonate-stimulated ATPase (HCO3(-)-ATPase) are localized in the mitochondria.

Further studies on the activation of microsomal (Na+ + k+)-atpase by a leukocytic product

Previous studies showed that microsomal (Na+ + K+)ATPase (ATP phosphohydrolase, EC 3.6.1.3) is activated by a proteinaeous material released by polymorphonuclear leukocytes. Investigations on the mode of action of the activator have been conducted by the siolation of 32P-labeled phosphoenzyme intermediates formed in the reaction of ATP and (Na+ + K)-ATPase, which has been postulated to occur through the formation and hydrolysis of acyl phosphate intermediates. The activator caused a concentration-dependent decrease in the recovery of phosphoenzyme intermediates that was not quantitatively altered by the Na+ or K+ concentration of the reaction mixture of by the presence of 1 mM oubain. A decline in phosphoenzyme intermediate recovery was promoted by the addition of the activator to preformed phosphoenzyme intermediates but not by activator that had been pretreated with protease or phenol. In addition, the activator caused a concentration-dependent stimulation of the p-nitrophenyl phosphatase and acetyl phosphatase activities of microsomal (Na+ + K+)-ATPase. It was proposed that the activator stimulates the dephosphorylation step of the (Na+ + K+)-ATPase reaction sequence.