The correlation between bismuth and uranyl staining and phosphorus content of intracellular structures as determined by electron spectroscopic imaging.

Four groups of intracellular structures can be recognized according to bismuth and uranyl staining and phosphorus content. (1) Those which contain phosphorus and stain strongly with uranyl acetate but not with bismuth (ribosomes, heterochromatin and mature ribosomal precursor granules), presumably because of their nucleic acid content. (2) Those which contain phosphorus and stain with uranyl acetate and bismuth (interchromatin granules, immature ribosomal precursor granules and mitochondrial granules), presumably because at least some of their phosphate is available to react with bismuth. (3) Those which contain little phosphorus but which stain strongly with bismuth and weakly with uranyl acetate (Golgi complex beads), perhaps because some ligand in addition to phosphate reacts with bismuth, and (4) those which do not contain phosphorus and stain with neither uranyl acetate nor bismuth (portasomes). Uranyl staining correlates strongly with the phosphorus content of nucleic acids, proteins and inorganic deposits. Bismuth will stain some phosphorylated molecules but not all. Thus only some phosphates stain with bismuth.