High recovery of nitrogenase activity and of 55 Fe-labeled nitrogenase in heterocysts isolated from Anabaena variabilis

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Abstract
Heterocysts were isolated from the N2-fixing cyanobacterium A. 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, approximately 5.0 .mu.mol (mg of chlorophyll a)-1 min-1 in the presence of H2 and light, accounted for an average of 60% of the nitrogenase activity of whole filaments, and was relatively insensitive to inactivation of O2. Soluble extracts derived from intact filaments grown with 55Fe, and from their heterocysts and vegetative cells, were subjected to electrophoresis. The nitrogenase and nitrogenase reductase bands (MoFe protein and Fe protein, or component I 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.