The quaternary structure of yeast aminopeptidase I. 2. Geometric arrangement of subunits.

Electron micrographs of native aminopeptidase I and of isolated subfragments were taken after negative staining with uranyl formate. From these studies and from the chemical evidence summarized in the preceding paper it is concluded that the active enzyme is a dodecamer possessing pseudo-D3 symmetry with the dimer as the smallest symmetric unit.