February 23, 2005 | David F. Coppedge

Clutch Enables Your Motors to Achieve 100% Efficiency

Those little ATP synthase motors (see 01/30/2005 entry) in your body and (in all living cells) made news again in Nature1 last week.  Scientists in Tokyo performed an ingenious set of experiments to measure the efficiency of the F1 synthesizing domain.  They attached a tiny magnet to the camshaft so that they could turn it with electromagnets at will, and they carefully measured the amount of ATP synthesized or hydrolyzed as the motor turned anticlockwise or clockwise under their control.  In the hydrolysis cycle, they found that the motor did not waste ATP; each molecule was successfully hydrolyzed with perfect efficiency, to the limits of their detection.
    A particular focus of their investigation was the role of the eta subunit, which is attached to the gamma camshaft.  During hydrolysis, the “downhill” function, it did not seem to matter whether eta was present or absent.  But in the “uphill” process (synthesizing ATP), it made a dramatic difference.  Without eta, each rotation produced, on average, only one product, but with it, they got three per revolution, with at least 77% efficiency.  The actual efficiency was probably higher, but was hard to measure for such small entities.  In best cases, it was 100%, they said: “Therefore our data point to an excellent mechanochemical coupling efficiency.  In the best cases, we observed the postulated value of three ATPs synthesized per turn.”
    “These results are consistent with the ubiquity of this strategic enzyme that fuels most of the energy consuming biological processes,” they said (emphasis added in all quotes).  “The present work reveals the unexpected importance of the eta-subunit in the synthesis of ATP.”  Though its precise function remains to be discovered, it was known to play a regulatory role; now, this team suspects it acts like a structural switch or clutch to lock the enzyme into synthesis mode.  Without it, the tiny motor undergoes wasteful slippage.
As a reminder to recent readers, you can find a wonderful animation of this molecular machine on the website of German biochemist Wolfgang Junge.  It is labeled “F0F1-ATPSynthase (animation)”  See also his Model Schematic.

1Rondelez et al., “Highly coupled ATP synthesis by F1-ATPase single molecules,” Nature 433, 773 – 777 (17 February 2005); doi:10.1038/nature03277.

By now, you expect our next observation: “The authors made no reference to evolution in their paper.”  They are treating these devices as actual mechanical motors, with stator, rotor, camshaft, and purposeful function, achieving performance stats beyond the dreams of human engineering.  Eat your heart out, David Hume.

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Categories: Cell Biology

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