Kinetic Mechanism of the SufC ATPase: THE CLEAVAGE STEP IS ACCELERATED BY SufB

Protein products of the suf operon are involved in iron-sulfur metabolism. SufC is an ATPase that can interact with SufB in the absence of nucleotide. We have studied the transient kinetics of the SufC ATPase mechanism using the fluorescent ATP analogue, 2'(3')-O-N-methylanthraniloyl-ATP (mantATP). mantATP initially binds to SufC weakly. A conformational change of the SufC·mantATP complex then occurs followed by the very slow cleavage of mantATP to mantADP and the rapid release of P[subscript i]. In the presence of SufB, the cleavage step is accelerated and the release of mantADP is inhibited. Both of these effects promote the formation of a SufC·mantADP complex. In the absence and presence of SufB, mantADP remains more tightly bound to SufC than mantATP. These studies provide a basis for how the SufB and -C proteins interact in the processes involved in regulating iron-sulfur transfer.