title: Calcium-ion binding to the chromaffin-granule surface.
abstract: 1. Ca(2+) ions decreased the surface charge of isolated adrenal-medullary chromaffin granules whether the granules were untreated or previously incubated with neuraminidase. 2. Ca(2+) binding in both cases followed a Langmuir adsorption isotherm. 3. The chromaffin-granule surface was essentially polyanionic with about 10800 anionic sites per granule, of which 4200 sites are capable of binding Ca(2+) ions with an electrochemical free energy of adsorption of -1.32kJ.mol(-1). 4. The surface region of the chromaffin granule was calculated to bind 1306 Ca(2+) ions at 2.2mm-Ca(2+) (ionic strength 0.16mol.litre(-1)). 5. The importance of Ca(2+) binding to the chromaffin-granule surface is discussed in relation to the hypothesis of secretion by exocytosis.
mesh_terms: D000313:Adrenal Medulla / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000378:metabolism; D007700:Kinetics; D008433:Mathematics; D009439:Neuraminidase; D009994:Osmolar Concentration; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism; D011955:Receptors, Drug; D013816:Thermodynamics
chemical_list: D011506:Proteins; D011955:Receptors, Drug; D009439:Neuraminidase; D002118:Calcium