ON STRUCTURE OF MITOCHONDRIA AND VALUE OF AMMONIUM MOLYBDATE AS A NEGATIVE STAIN FOR OSMOTICALLY SENSITIVE STRUCTURES

A number of osmotically sensitive structures have been found to be preserved intact without fixation when negatively stained with ammonium molybdate. This feature of ammonium molybdate has been evaluated by examining the structure of isolated ratliver mitochondria under a variety of conditions, and it appears to be related primarily to the tonicity of its solutions. Aqueous solutions, 2.0 % and 3.65 %, of ammonium molybdate are isosmotic with the media most commonly employed in the isolation of subcellular organelles (0.25 M and 0.44 M sucrose, respectively). Lithium and sodium tungstate have about half the osmolality of ammonium molybdate. All other negative stains at similar concentrations are highly hypoosmotic. The structure of mitochondria isolated from rat kidney, rabbit brown adipose tissue, blowfly flight muscles, and Paramecium negatively stained with ammonium molybdate is described. Ammonium molybdate also preserves the detailed structure of ribosomes, both free and attached to endoplasmic reticulum. © 1968 Academic Press, Inc.