Electron microscopy and image analysis of the multicatalytic proteinase

Abstract

On electron micrographs, negatively stained multicatalytic proteinase molecules are viewed end‐on (ring shaped) or side‐on (rectangular shaped). For aurothioglucose, ammonium molybdate‐ and phosphotungstate‐stained molecules, the dimensions measured are consistent. In contrast, uranyl acetate‐staining reveals ring‐shaped particles which vary in diameter between 12 and 16 nm. This is due to a partial collapse and substantial flattening of the structure. Digital image analysis of side‐on views of the particles reveals a tripartite, reel‐shaped structure. Within the ring‐like, end‐on projections of ammonium molybdate‐stained molecules six local centres of mass can be discerned; their position appears to depart, however, from a true six‐fold symmetry.