Binding and aggregation of pro-atrial natriuretic factor by calcium

Am J Physiol. 1992 Apr;262(4 Pt 1):C907-15. doi: 10.1152/ajpcell.1992.262.4.C907.

Abstract

Analysis of atrial secretory granule content by sodium dodecyl sulfate-gel electrophoresis followed by a 45Ca2+ overlay assay indicates that a 17,000 protein binds 45Ca2+. This protein, which can be immunostained by atrial natriuretic factor (ANF) antiserum, corresponds to proANF. Ca2+ binding is proportional to the amount of proANF and pH dependent. Generation of ANF-(1-98) by thrombin digestion of proANF does not affect Ca2+ binding. Blocking the carboxyl groups of proANF and the use of NH2-terminal fragments bearing those carboxyl groups demonstrated that the Ca(2+)-interaction site is probably located within the highly acidic portion (11-30) of the propeptide. Ca2+ binding to proANF induces its aggregation that can be verified by sedimentation. ProANF aggregation is Ca2+ dependent, being optimal at 10 mM, partially pH dependent, and greatly increased by high concentrations of proANF. However, because of its relatively low-binding affinity, Ca2+ can be substituted by other divalent cations such as Sr2+, Ba2+, or Mg2+. The high level of Ca2+ in atrial secretory granules and the aggregation of proANF in the presence of Ca2+ suggest a possible involvement of these physicochemical properties in the condensed state of the matrix of secretory granules. Indeed, detergent solubilization of the membrane of the secretory granules in presence of Ca2+ resulted only in a partial dissolution of the dense core matrix. We therefore postulate that, in the Golgi complex, proANF and Ca2+ associate to form a condensed aggregate that helps package secretory material into secretory vesicles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Atrial Natriuretic Factor / metabolism*
  • Calcium / metabolism
  • Calcium / pharmacology*
  • Cytoplasmic Granules / metabolism
  • Electrophoresis, Polyacrylamide Gel
  • Heart Atria
  • Humans
  • Microscopy, Electron
  • Myocardium / metabolism
  • Myocardium / ultrastructure
  • Osmolar Concentration
  • Protein Precursors / metabolism*

Substances

  • Protein Precursors
  • Atrial Natriuretic Factor
  • Calcium