Characterization of the palytoxin effect on Ca2+-ATPase from sarcoplasmic reticulum (SERCA)

Arch Biochem Biophys. 2008 Oct 1;478(1):36-42. doi: 10.1016/j.abb.2008.07.017. Epub 2008 Jul 24.

Abstract

The effect of palytoxin was studied in a microsomal fraction enriched in longitudinal tubules of the sarcoplasmic reticulum membrane. Half-maximal effect of palytoxin on Ca(2+)-ATPase activity yielded an apparent inhibition constant of approx. 0.4 microM. The inhibition process exhibited the following characteristics: (i) the degree of inhibition was dependent on membrane protein concentration; (ii) no protection was observed when the ATP concentration was raised; (iii) dependence on Ca(2+) concentration with a decreased maximum catalytic rate; (iv) it occurred in the absence of Ca(2+) ionophoric activity. Likewise, the inhibition mechanism was linked to: (i) rapid enzyme phosphorylation from ATP in the presence of Ca(2+) but lower steady-state levels of phosphoenzyme; (ii) more drastic effect on phosphoenzyme levels when the toxin was added to the enzyme in the absence of Ca(2+); (iii) decreased phosphoenzyme levels at saturating Ca(2+) concentrations; (iv) no effect on kinetics of phosphoenzyme decomposition. The palytoxin effect is related with lock of the enzyme in the Ca(2+)-free conformation so that progression of the catalytic cycle is impeded.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acrylamides / pharmacology*
  • Adenosine Triphosphate / chemistry
  • Animals
  • Calcium / metabolism
  • Calcium-Transporting ATPases / metabolism*
  • Catalysis
  • Cell Membrane / metabolism
  • Cnidarian Venoms
  • Female
  • Ionophores / pharmacology
  • Kinetics
  • Models, Biological
  • Phosphorylation
  • Rabbits
  • Sarcoplasmic Reticulum / metabolism
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases / metabolism

Substances

  • Acrylamides
  • Cnidarian Venoms
  • Ionophores
  • Adenosine Triphosphate
  • Sarcoplasmic Reticulum Calcium-Transporting ATPases
  • Calcium-Transporting ATPases
  • palytoxin
  • Calcium