Na-pump regulation by liponucleotides:its mechanism and physiological significance

A short-term regulation of Na,K-ATPase by the long-chain fatty acid esters and coenzyme A (liponucleotides) has been studied. It has been found that in the presence of liponucleotides the maximum velocity of ATP-hydrolysis doesn't change, but the apparent KM value decreases. While studying the ion transport it has been shown that palmitoyl-CoA stimulates the pump approaching the cell membrane from the cytoplasmic side, being an intracellular regulator of Na,K-ATPase. A possible mechanism of liponucleotide action on the process of enzyme functioning and its physiological implications is discussed.     

Transport ATPase: further studies on the properties of the thimerosal-treated enzyme.

Our previous studies showed that when ethylmercurithiosalicylate (thimerosal) interacts with the transport ATPase of the guinea pig kidney under specified conditions, the Na⁺ + K⁺-dependent ATPase activity is inhibited, while the Na⁺-dependent ATPase, the Na⁺ + ATP-dependent phosphorylation of the enzyme, and the K⁺-dependent discharge of the phosphoenzyme seem to be unaffected. Here we describe other properties of the thimerosal-treated enzyme: Na⁺-dependent ADP-ATP exchange, Na⁺-dependent UTPase, and K⁺-dependent p-nitrophenylphosphatase activities of the modified enzyme are not inhibited. Kinetics of the Na⁺ effect on the UTPase activities of the native and the modified enzyme are the same. However, K⁺ has a greater inhibitory effect on the Na⁺-UTPase of the modified enzyme than on the Na⁺-UTPase of the native enzyme. The increase in the apparent affinity of the thimerosal-treated enzyme for K⁺ is also evident from the kinetics of the K⁺ effect on p-nitrophenylphosphatase. Neither the native enzyme nor the modified enzyme catalyzes a P₁-ATP exchange. The uninhibited activities of the thimerosal-treated enzyme are sensitive to ouabain. These data provide further support for those reaction mechanisms in which the existence of two ATP sites within the enzyme is assumed.