An Adenosine Triphosphatase Isolated from Chromaffin-Granule Membranes is Closely Similar to F1-Adenosine Triphosphatase of Mitochondria

Abstract

1 An ATPase purified with high yield from bovine chromaffin granules closely resembles the mitochondrial F1-ATPase from bovine heart or bovine adrenal medulla with respect to the following properties: apparent molecular weight on gel filtration, subunit composition on dodecyl- sulphate/polyacrylamide gel electrophoresis, cross-reaction with an antiserum directed against F1-ATPase from bovine heart mitochondria, and proteolytic fingerprints of the three largest subunits. 2 The chromaffin granule ATPase could, however, be distinguished from the mitochondrial enzyme: it did not enhance the fluorescence of aurovertin and reacted differently from mitochondrial F1-ATPase in quantitative complement fixation. 3 The following three arguments make it unlikely that the ATPase isolated from chromaffin granules has been artifically dislodged from mitochondria during fractionation: (a) mitochondrial contamination of the purified chromaffin granule membranes was bhow 2%; (b) the purification procedure solubilized at least two thirds of the total ATPase activity of these membranes; (c) an antiserum directed against bovine mitochondrial F1-ATPase inhibited the ATP-driven uptake of 5-hydroxytryptamine by resealed chromaffin granule ‘ghosts’. 4 The proton-translocating ATPase of chromaffin granules is thus almost identical to mitochondrial F1-ATPase. This finding raises intriguing questions about the evolution of chromaffin granules and about the mechanisms by which the two enzymes are transported to different locations within the same cell.