Ribonuclease-gold labels proteoglycan-containing cytoplasmic granules and ribonucleic acid-containing organelles--a survey.

An enzyme-affinity-gold method to detect RNA in routinely prepared ultrastructural samples is based on the affinity of the gold-coupled enzyme, ribonuclease, for its substrate, RNA. High concentrations of a known inhibitor of RNase, heparin, are uniquely located in human mast cell granules. Specific labeling for the presence of heparin in these structures was determined using the RNase-gold (R-G) reagent based on the RNase inhibitor property of heparin. This property was used to probe for the presence of proteoglycans (PG) known to be present in a wide variety of ultrastructural samples, none of which contain heparin. In addition to known subcellular sites of RNA, the R-G reagent was shown to bind to PG-rich cytoplasmic granules in a wide variety of leukocytes and secretory cells of epithelial, endocrine, and neuroendocrine origin. This newly recognized property was used to image the changing distribution of labeled PGs during cellular maturation, secretion, and recovery from secretion of secretory cells in vivo, ex vivo, in vitro and in isolated, biochemically defined guinea pig basophil granule preparations.