Stepwise Energetics

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Science  18 Oct 2013:
Vol. 342, Issue 6156, pp. 290
DOI: 10.1126/science.342.6156.290-d

One fact that has been drilled into legions of introductory biochemistry students is that the hydrolysis of adenosine triphosphate (ATP) produces energy that is yoked to other reactions. What is less generally inculcated is that some of this energy can be extracted when ATP binds to proteins, in the form of conformational change, and that this can drive reactions too. In a study of nitrogenase, Duval et al. illustrate these two processes in a series of elegant kinetic measurements. They find that the interaction of the ATP-bound Fe protein and the MoFe protein triggers sequential electron transfer from the P cluster to the M cluster (both in the MoFe protein) and then from the Fe-S cluster in the Fe protein to the P cluster. Only after these transfers take place is the ATP hydrolyzed, and only after Pi is released can the ADP-bound Fe protein let go of the MoFe protein. This cycle repeats until the eight electrons needed to effect dinitrogen reduction (and hydrogen evolution) have been delivered. The distinction between binding and hydrolysis will remind biochemists of a certain age of the actomyosin ATPase.

Proc. Natl. Acad. Sci. U.S.A. 110, 10.1073/pnas.1311218110 (2013).

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