DINITROGENASE REDUCTASE-DEPENDENT AND MGATP-DEPENDENT MATURATION OF APODINITROGENASE FROM AZOTOBACTER-VINELANDII

The requirements for iron-molybdenum cofactor (FeMo-co) activation of apodinitrogenase from Azotobacter vinelandii strain UW97, which lacks dinitrogenase reductase activity as,assayed by substrate reduction, ha ve been examined. Activation of apodinitrogenase from strain UW97 by F eMo-co requires the addition of both dinitrogenase reductase and MgATP . When the same apodinitrogenase is pretreated with dinitrogenase redu ctase and MgATP and then partially purified, however, it does not requ ire these components for activation by FeMo-co. This suggests that din itrogenase reductase and MgATP are involved in processing apodinitroge nase to a FeMo-co activatable form. This processing step coincides wit h a change in the subunit composition of apodinitrogenase from alpha2b eta2 to a form with an additional subunit (gamma) attached. The apodin itrogenase with the associated gamma subunit is apparently the form of the protein that is competent for activation by FeMo-co.