Immunocytochemical localization of the soluble NAD‐dependent hydrogenase in cells of Alcaligenes eutrophus

The localization of the soluble NAD‐dependent hydrogenase in cells of Alcaligenes eutrophus PHB−4 was investigated using the protein A‐gold technique as a post‐embedding immunoelectron microscopic procedure. The enzyme was found throughout the cytoplasm of the cells. Autotrophic cells harvested in the logarithmic phase of growth exhibited a higher degree of labeling as compared to autotrophic cells from the stationary growth phase. Heterotrophic cells showed an almost identical labeling intensity in all growth phases. In a substrate‐shift experiment (from fructose to glycerol, performed in the stationary growth phase), high amounts of newly synthesized enzyme could be observed two hours after the shift. This enzyme was located, as inclusion bodies, in the DNA region of the cells.