PURIFICATION AND CHARACTERIZATION OF AN OXYGEN-STABLE FORM OF DINITROGENASE REDUCTASE-ACTIVATING GLYCOHYDROLASE FROM RHODOSPIRILLUM-RUBRUM

Dinitrogenase reductase-activating glycohydrolase (DRAG) is responsibl e for removing the ADP-ribose moiety from posttranslationally inactiva ted nitrogenase of Rhodospirillum rubrum. Using DRAG purified from an overexpressing strain (UR276), further properties of this enzyme were studied, including its u.v.-visible and fluorescence spectra and its s tability in air. DRAG appears to require no covalently bound inorganic cofactors for its activity or regulation. Previously, purified DRAG w as found to be rapidly inactivated in air. The air-catalysed lability originated with the presence of sodium dithionite and Mn2+ throughout the purification of the enzyme. This lability can be mimicked using H2 O2, which is known to oxidatively inactivate proteins containing bival ent metals. Implications for the regulation of nitrogenase are discuss ed with respect to the lack of sensitivity to air of the regulatory en zyme, DRAG.