Abstract
Heterocysts were isolated from the N(2)-fixing cyanobacterium Anabaena variabilis after vegetative cells were disrupted by treatment with lysozyme and cavitation in a sonic cleaning bath. The acetylene-reducing (nitrogenase) activity of the isolated heterocysts, ca. 5.0 mumol (mg of chlorophyll a)(-1) min(-1) in the presence of H(2) and light, accounted for an average of 60% of the nitrogenase activity of whole filaments, and was relatively insensitive to inactivation by oxygen. Soluble extracts derived from intact filaments grown with (55)Fe, and from their heterocysts and vegetative cells, were subjected to electrophoresis. The nitrogenase and nitrogenase reductase bands (MoFe protein and Fe protein, or component 1 and component 2, respectively) were identified in these nondenaturing gels, and their radioactivities were quantitated. The isolated heterocysts accounted for an average of 91% of the nitrogenase and 69% of the nitrogenase reductase of the original filaments.