Kinetic attributes of rat liver microsomal adenosine 5' triphosphate phosphohydrolase (ATPase).
The kinetic properties of the rat liver microsomal ATPase, with respect to Na(+), K(+) and AT P requirements were examined. Presence of Na(+) and K(+), or both hardly caused any stimulation of the enzyme activity. The Km values for Na(+) and K(+) were substantially low (0.32 and 0.05 mM, respectively), compared to those reported for the Na(+), K(+) ATPasesfrom different tissues. Substrate kinetics studies revealed that in the absence of Na(+) and K(+), ATP is an activator of the enzyme. The enzyme displayed increased activity with increase in the energy of activation in the absence of Na(+) and K(+). The activity was partially inhibited by ouabain only in the presence of Na(+) and K(+). The results suggest that the liver microsomal enzyme is not a Na(+), K(+) ATPase, but has requirement of monovalent cations for the regulation of its activity. Also, the beta3 subunit of the enzyme has a Km lowering effect.
Department of Biochemistry, Faculty of Science, M. S. University of Baroda, Vadodara, 390 002, India.
Subhash D
SD
Katewa
Surendra S
SS
Katyare
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D011188:Potassium / Q000378:metabolism; D021122:Protein Subunits / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism
D021122:Protein Subunits; D000255:Adenosine Triphosphate; D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium