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PDBsum entry 2bcn
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Oxidoreductase/electron transfer
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PDB id
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2bcn
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References listed in PDB file
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Key reference
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Title
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Solvent isotope effects on interfacial protein electron transfer in crystals and electrode films.
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Authors
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S.A.Kang,
K.R.Hoke,
B.R.Crane.
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Ref.
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J Am Chem Soc, 2006,
128,
2346-2355.
[DOI no: ]
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PubMed id
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Abstract
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D(2)O-grown crystals of yeast zinc porphyrin substituted cytochrome c peroxidase
(ZnCcP) in complex with yeast iso-1-cytochrome c (yCc) diffract to higher
resolution (1.7 A) and pack differently than H(2)O-grown crystals (2.4-3.0 A).
Two ZnCcP's bind the same yCc (porphyrin-to-porphyrin separations of 19 and 29
A), with one ZnCcP interacting through the same interface found in the H(2)O
crystals. The triplet excited-state of at least one of the two unique ZnCcP's is
quenched by electron transfer (ET) to Fe(III)yCc (k(e) = 220 s(-1)). Measurement
of thermal recombination ET between Fe(II)yCc and ZnCcP+ in the D(2)O-treated
crystals has both slow and fast components that differ by 2 orders of magnitude
(k(eb)(1) = 2200 s(-1), k(eb)(2) = 30 s(-1)). Back ET in H(2)O-grown crystals is
too fast for observation, but soaking H(2)O-grown crystals in D(2)O for hours
generates slower back ET, with kinetics similar to those of the D(2)O-grown
crystals (k(eb)(1) = 7000 s(-1), k(eb)(2) = 100 s(-1)). Protein-film voltammetry
of yCc adsorbed to mixed alkanethiol monolayers on gold electrodes shows slower
ET for D(2)O-grown yCc films than for H(2)O-grown films (k(H) = 800 s(-1); k(D)
= 540 s(-1) at 20 degrees C). Soaking H(2)O- or D(2)O-grown films in the counter
solvent produces an immediate inverse isotope effect that diminishes over hours
until the ET rate reaches that found in the counter solvent. Thus, D(2)O
substitution perturbs interactions and ET between yCc and either CcP or
electrode films. The effects derive from slow exchanging protons or solvent
molecules that in the crystal produce only small structural changes.
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