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Research ArticleArticle

Effects of Phlorizin on Membrane Cation-Dependent Adenosine Triphosphatase and p-Nitrophenyl Phosphatase Activities

JOSEPH D. ROBINSON
Molecular Pharmacology November 1969, 5 (6) 584-592;
JOSEPH D. ROBINSON
Department of Pharmacology, State University of New York, Upstate Medical Center, Syracuse, New York 13210
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Abstract

Phlorizin stimulated the K+-dependent phosphatase activity (measured with p-nitrophenyl phosphate) but inhibited the (Na+ + K+)-dependent adenosine triphosphatase activity in an enzyme preparation obtained from rat brain. The concentration of phlorizin required for half-maximal stimulation of the phosphatase was 0.05 mM, whereas the Ki for the ATPase was 0.06 mM. Of a series of hydroxylated aromatic compounds, phloretin alone also stimulated the phosphatase.

With the phosphatase, 0.03 mM phlorizin decreased the concentration of KCl required for half-maximal velocity (K0.5) from 1.92 to 1.17 mM but had little effect on Vmax. Na+ inhibited the phosphatase, and phlorizin increased the Ki for NaCl, from 6 to 12 mM. With the ATPase, 0.1 mM phlorizin similarly decreased the K0.5 for KCl, from 0.74 to 0.48 mM, and increased the K0.5 for NaCl, from 5.0 to 10.5 mM. The positive cooperative allosteric response to Na+, as indicated by the Hill plot with n > 1, was also converted to a negative cooperative response. In addition, phlorizin inhibited the Na+-dependent phosphorylation of the enzyme.

These data indicate that phlorizin reacts similarly with the cation-dependent ATPase and phosphatase, serving as a heterotropic allosteric modifier to increase the apparent affinity toward K+ but to decrease it toward Na+. These findings further imply that the phosphatase represents an aspect of the over-all ATPase reaction. Finally, the data raise the possibility that the inhibition of sugar transport by phorizin and phloretin may be mediated in part through an effect on the Na+-dependent aspects of that transport system.

ACKNOWLEDGMENT The proficient technical assistance of Mrs. Shelly Buzzard is gratefully acknowledged.

  • Copyright ©, 1969, by Academic Press Inc.

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Molecular Pharmacology
Vol. 5, Issue 6
1 Nov 1969
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Research ArticleArticle

Effects of Phlorizin on Membrane Cation-Dependent Adenosine Triphosphatase and p-Nitrophenyl Phosphatase Activities

JOSEPH D. ROBINSON
Molecular Pharmacology November 1, 1969, 5 (6) 584-592;

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Research ArticleArticle

Effects of Phlorizin on Membrane Cation-Dependent Adenosine Triphosphatase and p-Nitrophenyl Phosphatase Activities

JOSEPH D. ROBINSON
Molecular Pharmacology November 1, 1969, 5 (6) 584-592;
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