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Abstract
Abstract l-Ribulose 5-phosphate 4-epimerase has been crystallized from l-arabinose-induced cells of Escherichia coli B/r strain F' araB-24/araB-24 after a 40-fold purification. The enzyme is homogeneous in the ultracentrifuge and 98% pure by acrylamide gel disc electrophoresis. The molecular weight determined by sedimentation equilibrium is 1.03 ± 0.01 x 105. The enzyme is free of d-ribulose 5-phosphate 3-epimerase activity, does not exhibit any cofactor requirement, and shows maximal activity from pH 7 to 10. An amino acid analysis is presented.
Highlights
Blank containing no enzyme, but treated in the same manner, served as a control. Results of this two-step assay agree with that of the single step assay within experiment.al error
The concentrations of pure 4-epimerase solutions were determined with either the Lowry method that had been calibrated on a dry weight basis as previously described (7) or by their absorbances at 280 mp, with a specific absorbance value of
The sonically disrupted suspension was centrifuged for 1 hour at 56,000 x g in a Spinco model L ultracentrifuge
Summary
The synthesis of L-arabinosc isotncrase, L-ribulokinase, and L-ribulose 5-phosphate 4-epimerase have been shown to bc coordinate (3, 5). I~-24/:tralI-24 (4) grown in cascin hydrolysate L-urabinose tnediutn This mutant, selected for its increased ettzyme l)roduction, has been cultured under similar conditions to serve as a source of L arabinose isomerase (7). L-Ribulose S-Phosphate 4-Epimerase Assay-The spcctrophotometric assay was essentially as previously described (1). A blank containing no enzyme, but treated in the same manner, served as a control Results of this two-step assay agree with that of the single step assay within experiment.al error. The concentrations of pure 4-epimerase solutions were determined with either the Lowry method that had been calibrated on a dry weight basis as previously described (7) or by their absorbances at 280 mp, with a specific absorbance value of. All other reagents were the best obtainable grade from commercial sources
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