The distribution of Mg2+ ATPase and its loss of specific activity upon gradient centrifugation of isolated chromaffin granules.

Preparations of purified chromaffin granules were subjected to isopycnic sucrose gradient centrifugation. Determination of Mg2+ ATPase activity and catecholamines showed that the distribution of ATPase almost parallelled the distribution of catecholamines. The distribution of ATPase was slightly shifted to lower densities and was suggested to be caused by the heterogeneity of the chromaffin granules. The results therefore provide evidence that ATPase is associated with chromaffin granules. Determination of the recovery of ATPase activity upon gradient centrifugation revealed losses of enzyme activity which were found to be proportional to the dilutions of the granule preparation subjected to gradient centrifugation.