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PDBsum entry 2acq
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Oxidoreductase
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PDB id
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2acq
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References listed in PDB file
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Key reference
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Title
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An anion binding site in human aldose reductase: mechanistic implications for the binding of citrate, Cacodylate, And glucose 6-Phosphate.
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Authors
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D.H.Harrison,
K.M.Bohren,
D.Ringe,
G.A.Petsko,
K.H.Gabbay.
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Ref.
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Biochemistry, 1994,
33,
2011-2020.
[DOI no: ]
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PubMed id
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Abstract
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Aldose reductase is a NADPH-dependent aldo-keto reductase involved in the
pathogenesis of some diabetic and galactosemic complications. The published
crystal structure of human aldose reductase [Wilson et al. (1992) Science 257,
81-84] contains a hitherto unexplained electron density positioned within the
active site pocket facing the nicotinamide ring of the NADPH and other key
active site residues (Tyr48, His110, and Cys298). In this paper we identify the
electron density as citrate, which is present in the crystallization buffer (pH
5.0), and provide confirmatory evidence by both kinetic and crystallographic
experiments. Citrate is an uncompetitive inhibitor in the forward reaction with
respect to aldehyde (reduction of aldehyde), while it is a competitive inhibitor
with respect to alcohol in the backward reaction (oxidation of alcohol),
indicating that it interacts with the enzyme-NADP(+)-product complex. Citrate
can be replaced in the crystalline enzyme complex by cacodylate or glucose
6-phosphate; the structure of each of these complexes shows the specific
molecule bound in the active site. All of the structures have been determined to
a nominal resolution of 1.76 A and refined to R-factors below 18%. While
cacodylate can be bound within the active site under the crystallization
conditions, it does not inhibit the wild-type enzyme in solution. Glucose
6-phosphate, however, is a substrate for aldose reductase. The similar location
of the negative charges of citrate, cacodylate, and glucose 6-phosphate within
the active site suggests an anion-binding site delineated by the C4N of
nicotinamide, the OH of Tyr48, and the N epsilon of His110. The location of
citrate binding in the active site leads to a plausible catalytic mechanism for
aldose reductase.
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Secondary reference #1
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Title
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An unlikely sugar substrate site in the 1.65 a structure of the human aldose reductase holoenzyme implicated in diabetic complications.
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Authors
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D.K.Wilson,
K.M.Bohren,
K.H.Gabbay,
F.A.Quiocho.
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Ref.
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Science, 1992,
257,
81-84.
[DOI no: ]
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PubMed id
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