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Title: Kinetic attributes of rat liver microsomal adenosine 5’ triphosphate phosphohydrolase (ATPase)
Authors: Katewa, Subhash D
Katyare, Surendra S
Keywords: Liver microsomal ATPase
⍺1β3 subunits
substrate kinetics
ouabain inhibition
Issue Date: Aug-2003
Publisher: CSIR
Abstract: The kinetic properties of the rat liver microsomal ATPase, with respect to Na<sup>+</sup>, K<sup>+</sup> and ATP requirements were examined. Presence of Na<sup>+</sup> and K<sup>+</sup> or both hardly caused any stimulation of the enzyme activity. The Km values for Na<sup>+</sup> and K<sup>+</sup>were substantially low (0.32 and 0.05 mM, respectively), compared to those reported for the Na<sup>+</sup>, K<sup>+</sup> ATPases from different tissues. Substrate kinetics studies revealed that in the absence of Na<sup>+</sup> and K<sup>+</sup>, ATP is an activator of the enzyme. The enzyme displayed increased activity with increase in the energy of activation in the absence of Na<sup>+</sup> and K<sup>+</sup>. The activity was partially inhibited by ouabain only in the presence of Na<sup>+</sup> and K<sup>+</sup>. The results suggest that the liver microsomal enzyme is not a Na<sup>+</sup>, K<sup>+</sup> ATPase, but has requirement of monovalent cations for the regulation of its activity. Also, the β3 subunit of the enzyme has a K<sub>m</sub> lowering effect.
Description: 252-259
ISSN: 0301-1208
Appears in Collections:IJBB Vol.40(4) [August 2003]

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