Negative staining is very useful, but typically produces a resolution level of 20-25A and thus reveals only the quaternary level of protein structure. The recent finding that heavy metals are not required to obtain sufficient contrast for direct TEM imaging has led to examinations of various light atom compounds in a search for new unconventional staining agents having improved properties that can lead to higher resolution. This report examines whether the acetate salt of a divalent cation, magnesium, can function successfully for experimental negative staining.

Magnesium acetate (Mg(C2H3O2)2˙4H2O) (F.W. = 214.5) was used as an aqueous solution at 200mM. Bovine liver catalase crystals were examined as test specimens under standardized conditions. Suspended crystals were deposited onto a hydrophilic thin carbon supporting film and then were negatively stained by the on-grid procedure described previously. Imaging at l00kV used a JEOL 100-CX transmission electron microscope with Kodak S0-163 film.