Ultrastructural localization of delta 5-3 beta-hydroxysteroid dehydrogenase in the interrenal cells of the goldfisch (Carassius auratus).

The ultrastructural localization of the enzyme delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) was studied in the goldfish interrenal cells by using the potassium ferricyanide method. Immersion fixation in a mixture of 1% paraformaldehyde and 0.25% glutaraldehyde results in a consistently good ultrastructural preservation and enzyme localization. A precipitate of copper ferrocyanide indicating the localization of 3 beta-HSD activity was observed in close vicinity to the smooth endoplasmic reticulum or in contact with the outer surface of its membrane. A small number of precipitated grains were also found in the lumen of mitochondrial cristae. Addition of phenazine methosulfate increased the intensity of the reaction without changing the localization of the copper ferrocyanide grains. The findings suggest that the outer surface of the smooth endoplasmic reticulum is the major site of 3 beta-HSD activity in goldfish interrenal cells.