Kinetics of irreversible activation of adenylate cyclase of fat cell membranes by phosphonium and phosphoramidate analogs of gtp1.

Journal Article (Journal Article)

The ability of guanylylimidodiphosphate (GMP=P(NH)P) and guanylylmethylenediphosphonate (GMP-P(CH2)P) to activate adenylate cyclase activity has been studied by incubating these analogs with fat cell membranes followed by thorough washing of the membranes before assay of enzyme activity. GMP-P(NH)P is hydrolyzed by membrane preparations from several tissues. A pyruvate kinase regenerating system maintains the concentration of GMP-P(NH)P and thereby augments the ability of suboptimal concentrations of GMP-P(NH)P to activate adenylate cyclase. GTP inhibits activation of fat cell membrane adenylate cyclase by GMP-P(NH)P but this inhibition is overcome by time. This is consistent with the virtually irreversible nature of the GMP-P(NH)P activation, and with the inability of GTP to reverse the stimulated state of the enzyme. Although the initial rate of enzyme activation is highly dependent on the concentration of GMP-P(NH)P, with increasing times of incubation nearly the same maximal extent of activation is seen over a wide range of concentrations. Thus, it is not possible to estimate true affinity constants (at equilibrium) for GMP-P(NH)P, as anticipated from the virtually irreversible character of the activation process.

Full Text

Duke Authors

Cited Authors

  • Jacobs, S; Bennett, V; Cuatrecasas, P

Published Date

  • July 1, 1976

Published In

Volume / Issue

  • 2 / 4

Start / End Page

  • 205 - 223

PubMed ID

  • 184121

International Standard Serial Number (ISSN)

  • 0095-1544


  • eng

Conference Location

  • United States