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Change in stereospecificity of bovine lens aldose reductase modified by oxidative stress.
No full textBovine lens aldose reductase (alditol:NADP+ oxidoreductase, EC 1.1.1.21) undergoes an oxidative modification, greatly stimulated by high ionic strength, upon incubation in the presence of oxygen radical generating systems (Del Corso, A., Camici, M., and Mura, U. (1987) Biochem. Biophys. Res. Commun. 148, 369-375). The enzyme modification is accompanied by a change in stereospecificity toward the two enantiomers of glyceraldehyde. In particular, the Km for L-glyceraldehyde of the native form increased over 150 times after the enzyme modification, with a decrease in the catalytic efficiency of over 200 times. By contrast, for the D-enantiomer the Km increased only 7 times with respect to the native form, with a concomitant decrease in the catalytic efficiency of only approximately 3 times. This dramatic change in stereospecificity may account for the reported apparent cooperative behavior exhibited also by highly purified electrophoretically homogeneous preparations of aldose reductase.[...
Utilization of exogenous purine compounds in Bacillus cereus: translocation of the ribose moiety of inosine
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Spectrophotometric determination of ribose 1-phosphate
No full textIn the course of studies on nucleoside monophosphate metabolism, the need was encountered for a method to determine ribose-1-phosphate. Published assays for ribose-1-phosphate depend either on chromatographic separation of the sugarphosphate, or else on its acid lability which allows it to be determined as a phosphate. The present work describes a less laborious spectrophotometric assay which is both rapid and specific. The basis of the method is the absorbance change at 265 nm associated with the following two-stage enzymatic conversion: ribose-1-phosphate + adenine phosphate + adenosine (adenosine phosphorylase); adenosine + H2O → inosine + NH3 (adenosine deaminase). The change in absorbance was proportional to ribose-1-phosphate concentration at least up to 25 μg/ml. In tests of the assay, it was possible to detect ribose-1-phosphate formation from inosine and phosphate catalyzed by purine nucleoside phosphorylase. Further, the degradation of ribose-1-phosphate by various commercial phosphatases and several tissues or microbial extracts was observed
The standard Gibbs free energy change of hydrolysis of ribose-1-phosphate
No full textThe standard Gibbs free energy change of hydrolysis of α-d-ribose 1-phosphate has been measured at pH 7.0, ionic strength 0.1 m, and 25 °C by combining the corresponding values of the two following reactions: adenosine + H2O ág adenine + ribose (ΔG0′ = −2.3 ± 0.1 kcal/mol), catalyzed by adenosine nucleosidase, and ribose 1-phosphate + adenine ág adenosine + Pi (ΔG0′ = −3.1 ± 0.1 kcal/mol), catalyzed by adenosine phosphorylase. The standard Gibbs free energy changes were calculated for both reactions from the equilibrium constant. A value of -5.4 ± 0.15 kcal/mol, comparable to that of other hemiacetal phosphoric esters, was obtained for the hydrolysis of ribose 1-phosphate
Adenosine phosphorylase from vegetative forms and free spores of Bacillus subtilis: properties and possible physiological role
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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