MOLYBDENUM ACCUMULATION AND STORAGE IN KLEBSIELLA-PNEUMONIAE AND AZOTOBACTER-VINELANDII

In K. pneumoniae, Mo accumulation appeared to be coregulated with nitrogenase synthesis. O2 and NH4+, which repressed nitrogenase synthesis, also prevented Mo accumulation. In A. vinelandii, Mo accumulation did not appear to be regulated. Mo was accumulated to levels much higher than those seen in K. pneumoniae even when nitrogenase synthesis was repressed. Accumulated Mo was bound mainly to a Mo storage protein and could act as a supply for the Mo needed in component I synthesis when extracellular Mo was exhausted. When A. vinelandii was grown in the presence of WO42- rather than MoO42-, it synthesized a W-containing analog of the Mo storage protein. The Mo storage protein was purified from NH4+ and N2-grown cells of A. vinelandii and was a tetramer of 2 pairs of different subunits binding a minimum of 15 atoms of Mo/tetramer.