The grid sectioning technique: a study of catalase platelets.

The grid sectioning technique has been used to obtain the two missing principal axis projections of orthorhombic catalase platelets and to measure directly the unit cell c-value. The negatively stained platelets have a unit cell c-dimension of half that proposed by Unwin (1975) from powder X-ray diffraction. The precision of the grid sectioning technique in positioning sections along a specimen axis shows that the growth fault lines usually observed on negatively stained catalase platelets are rows of missing molecules filled with stain. From these sections conclusions are drawn concerning the action of negative stain on a specimen, the microtomy process, and the specimen/supporting film interaction. Finally the value of microtomy for detailed structural analysis of biological objects is emphasized.