Biochemistry

Air Tight

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Science  20 Aug 2004:
Vol. 305, Issue 5687, pp. 1079
DOI: 10.1126/science.305.5687.1079a

A recent theme in explanations of the catalytic efficacy of protein enzymes is the harnessing of correlated fluctuations (at the atomic scale) of the polypeptide backbone and amino acid side chains. In some cases, these motions would serve to align and reposition chemically powerful groups within the active site, whereas in other cases, they would act to control the entry of reactants and exit of products.

Salomonsson et al. assess just how snug the entryway into the cytochrome c oxidase catalytic center is; this enzyme uses four electrons and four protons to transform gaseous O2 into liquid H2O. Using CO as an inactive analog of O2, they find that adding a three-carbon unit (by swapping valine for glycine) obstructs access, implying that fluctuations, at least in this portion of the enzyme, are constrained to the extent that a diatomic gas cannot squeeze through. — GJC

Proc. Natl. Acad. Sci. U.S.A. 101, 11617 (2004).

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