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Reviews

of books by Peter M. Hoffmann

PETER M. HOFFMANN is a professor of Physics and associate Dean at the College of Liberal Arts & Sciences at Wayne State University, Michigan, where he leads a Nanomechanics Laboratory. His research interests are in molecular machines using atomic force microscopy.

Life's Ratchet: How Molecular Machines extract Order from Chaos
by Peter M Hoffmann
Basic Books, 2012

This book is an excellent primer for everyone interested in how molecular machines, the macromolecules (enzymes, transporters, polymerases, pumps, motors and rotors) that life employs to power it's cells, work. It is not a textbook explaining only mechanisms, but a description of how these nanometer scaled protein complexes transform any form of energy available to the cell into cellular work by exploiting the intrinsic kinetic energy of the 'molecular storm', a term coined by Hoffmann. In his description, the random microscopic motion of atoms and small molecules (diffusion) is channeled into directed macroscopic motion of proteins, whose structures have built-in geometric constraints that direct their movements, i.e., they operate as (mostly) irreversible ratchets.

For me, one of the most useful insight from this book is the discussion of the nanoscale as an optimal range for energy conversion mechanisms. To synthesize a chemical bond costs about the same amount of energy as bending a protein, which is just about the same as the kinetic energy of the 'molecular storm'. Motion from the kinetic energy of water molecule is random, of course, so how can these nanomachines avoid chaos or reversible random reactions? Here is where Hoffmann gives plenty of excellent examples, focusing mostly on kinesin and myosin motor complexes, but also on the ATP synthase (rotor). My favorite example, ion pumping is mentioned, but not in any detail. Anyway, all these molecular machines work the same way, explaining the power of the induced fit mechanism of enzyme catalysis. In the case of ion transport across membranes, the energy released from ATP hydrolysis causes a conformational change in an ion pump (e.g. the Na/K pump) powering the rocker switch ratchet of these membrane transporters.