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Aldehyde reductase, a member of the aldo-keto reductase superfamily, catalyzes the NADPH-dependent reduction of a variety of aldehydes to their corresponding alcohols. The structure of porcine aldehyde reductase-NADPH binary complex has been determined by x-ray diffraction methods and refined to a crystallographic R-factor of 0.20 at 2.4 A resolution. The tertiary structure of aldehyde reductase is similar to that of aldose reductase and consists of an alpha/beta-barrel with the active site located at the carboxy terminus of the strands of the barrel. Unlike aldose reductase, the N epsilon 2 of the imidazole ring of His 113 in aldehyde reductase interacts, through a hydrogen bond, with the amide group of the nicotinamide ring of NADPH.

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The effect of several metal ions on the production of diphtheria toxin was tested. By using the gel immunodiffusion system for detecting toxin, a wide range of metal ion concentrations was conveniently surveyed. Five divalent cations, Fe2+, Cu2+, Co2+, Ni2+, and Mn2+ inhibited toxin production within a range of concentrations that did not inhibit growth of the producing strain. Growth and toxin production were inhibited at identical concentrations by both Cd2+ and Zn2+, whereas A13+ and Sr2`affected neither growth nor toxin production over the range of concentrations tested. The data showed that Fe2+ was the most

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