The character of the stored molecules in chromaffin granules of the adrenal medulla: A nuclear magnetic resonance study

The organization of the internal contents of bovine adrenal chromaffin granules has been studied using nuclear magnetic resonance spectroscopy. The method permits an examination of the interactions between adenosine triphosphate, metal ions, adrenaline and the chromogranin proteins. Particular advantage accrues when the naturally occurring cations, magnesium and calcium are replaced by manganese cations, since, as shown here, the manganous ion is an effective perturbing probe of structure. The nuclear magnetic resonance spectrum of the protein in the vesicles is compared with that of the isolated proteins.The results show that there is a loose network of interactions between the various components. The major part of the network is the interaction of the chromogranin protein, shown to have approximately a random coil conformation, with the adenosine triphosphate and the adrenaline. The purpose of the organized loose structure would appear to be to lower osmotic pressure without hindering rapid release of the vesicle contents on breaking the membrane.