Binding of catecholamines to phospholipids isolated from adrenal medullary granules.

The large granules of the adrenal medullary fraction were lysed and subjected to Sepharose 2B gel filtration. Proteophospholipids (PPL) were isolated from the membrane fraction and used for binding of catecholamines (CA), such as noradrenaline (NA), adrenaline (A) and dopamine (DA). The affinity order was DA greater than NA = A. The binding capacity was dependent on amine concentration, pH and ionic strength, and amounted to about 2 and 3.5 mumol per mumol lipid phosphorus in ether and ether-ethanol, respectively. A Scatchard plot revealed only one type of binding site; Kd = 8.3 mM. The anionic detergent sodium dodesylsulphonate (SDS) moderately increased the uptake of NA and A while cationic detergents like cetyltrimethylammonium bromide (CTAB) and Hyamine 2389 strongly diminished the binding to PPL. The ionic detergent sodium deoxycholate (DOC) and the non-ionic detergent Triton X-100 were without significant effect. It is suggested that the dipolar head group of the granule lipids, particularly the lipid phosphate groups, are involved in electrostatic or complex interactions with the CA, either directly, or through water molecules within the lipid polar head group.