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Perseitol, Demonstrating Its Requirement for Ribitol Xylitol D-A Rabitol Substrates Bearing the D-Manno Configuration

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Perseitol, Demonstrating Its Requirement for Ribitol Xylitol D-A Rabitol Substrates Bearing the D-Manno Configuration POLYOL DEHYDROGENASES OF AZOTOBACTER AGILIS LEON MARCUS AND ALLEN G. MARR Department of Bacteriology, University of California, Davis, California Received for publication February 16, 1961 ABSTRACT differ in chain length and configuration are MARCUS, LEON (University of California, available either as natural products or can be Davis), AND ALLEN G. AIARR. Polyol dehydro- obtained by reduction of corresponding sugars; genases of Azotobacter agilis. J. Bacteriol. 82: the availability of such an array of compounds 224-232. 1961.-Two soluble diphosphopyridine- may facilitate a more precise definition of the linked polyol dehydrogenases are formed by structural specificity of induction and of enzyme Azotobacter agilis (A. vinelandii). The first, activity. The structures of some of the polyols D-mannitol dehydrogenase is induced by D- which are most significant in this investigation mannitol and all of the pentitols except L-arabitol. are as follows: Ribitol is an excellent inducer of mannitol CH20H CH2 OH CH20H dehydrogenase it is not although metabolized, H-C-OH H-C-( nor does the enzyme act upon it. This allows OH HO-C-H study of the gratuitous induction of mannitol H-C-OH HFO-C-lHI HO-C-H dehydrogenase. H-C-OH H-C-(3H H-C-OH Of the polyols tested, mannitol dehydrogenase oxidizes D-mannitol, D-arabitol, D-rhamnitol, and CH20H CH2 OH CH20H perseitol, demonstrating its requirement for Ribitol Xylitol D-A rabitol substrates bearing the D-manno configuration. (D-lyXitol) The corresponding 2-ketoses, D-fructose, D- xylulose, and presumably D-rhamnulose, and CH 20H CH20H perseulose are reduced. CH20H HO-C--H H-C-OH The second enzyme, L-iditol dehydrogenase is H-C-OH HO-C-H HO-C-H induced only by polyols containing the D-Xy10 configuration, i.e., sorbitol and xylitol. L-Iditol H-C-OH H-C-OH H-C-OH dehydrogenase oxidizes D-Xy10 polyols seven HO-C-H H-C-iOH H-C-OH times faster than it does D-ribo polyols. Sub- strates oxidized include L-iditol, sorbitol, xylitol, CH20H CH220H CH20H and ribitol. The corresponding 2-ketoses, L- L-Arabitol D-Manni"tol Sorbitol (D- (L-lyXitol) glucitol or sorbose, D-fructose, D-xylulose, and D-ribulose, L-gUlitol) are reduced. The two polyol dehydrogenases have been CH20H CH2OH separated and purified by chromatography on a modified cellulose ion exchanger. H-C-OH H-C-OH HO-C-H HO-C-H This work was begun with the intent of char- HO-C-H H-C-OH acterizing a soluble inducible enzyme suitable H-C-OH HO-C-H for the study of the kinetics of induction of enzymes in the azotobacter. Polyol dehydro- CH20H CH20H genases seemed a reasonable choice for two Dulcitol L-lditol reasons. First, Burris, Phelps, and Wilson (1943) (galactitol) had established that the metabolism of mannitol This paper reports the specificity of induction was inducible in Azotobacter agilis (A. vinelandii and activity of two distinct polyol dehydro- strain 0). Second, a wide variety of polyols which genases produced by A. agilis, D-mannitol and 224 19611 POLYOL DEHYDROGENASES 225 L-iditol dehydrogenases. The purification of assay buffer and held at 30 C. To a 1-cm silica D-mannitol dehydrogenase and the kinetics of absorption cell were added in order: 2.3-x ml of its induction will be discussed elsewhere. 0.05 M tris chloride buffer, pH 8.6; 0.5 ml of 0.5 M polyol; and x ml of enzyme preparation. MATERIALS AND METHODS Ordinarily, sufficient enzyme was added to give a Culture. A. agilis (A. vinelandii strain 0) was change in absorbancy at 340 m,u of 0.1 to 0.35 grown in Burk's nitrogen-free medium (Wilson per min. If the activity was low, a maximum of and Knight, 1952) modified by reducing the 0.5 ml of enzyme preparation was added, and calcium concentration, to contain the following the rate obtained was reported. Addition of 0.2 per liter of distilled water: K2HPO4, 0.8 g; ml of 0.02 M DPN started the reaction. KH2PO4, 0.2 g; MgSO4-7H20, 0.2 g; CaSO4- The reduction of ketose was measured by 2H20, 0.025 g; Na2MoO4*2H20, 0.00025 g; following the oxidation of DPNH. To a 1-cm FeNH4 (S04)2-12H20, 0.0086 g; sucrose, 20.0 g. absorption cell were added in order: 2.4-x ml of The phosphate, sulfate, iron, and molybdate 0.05 M tris chloride buffer, pH 8.6; 0.5 ml of salts were dissolved separately. The solutions 0.5 M ketose; and x ml enzyme. The reaction was were combined to give a medium free of turbidity, started by adding 0.1 ml of a freshly prepared 100 ml of which were dispensed per 250-ml solution of DPNH containing 2 mg DPNH per Erlenmeyer flask. During autoclaving, a slight ml of buffer. precipitate forms which dissolves completely Formation or disappearance of DPNH was on cooling. followed at 340 m, with a spectrophotometer, Inocula were taken from cultures growing the cell compartment of which was maintained exponentially with a specific growth rate of at 30 C. The spectrophotometer has been modified approximately 0.3 per hour. Cultures were for recording. The current of, the phototube was incubated on a rotary shaker at 30 C and har- amplified by a Kiethly electrometer, model 610. vested during the late logarithmic phase by The output of the electrometer, which is pro- centrifugation at 5,000 X g for 5 min. portional to per cent transmission, was converted Cell-free extracts. The enzymes were released to absorbancy by a diode analogue and recorded from the cells by osmotic shock (Robrish and by a Varian strip chart recorder, model G-11. Marr, 19"7). An equal volume of 2 M glycerol was Since kinetics for oxidation of polyol are zero added to the centrifuged pellet of cells and order, units of enzymatic activity can be esti- mixed thoroughly in the 50-ml plastic centrifuge mated directly from the slope of the recorded tube. After allowing at least 1 min for glycerol to change in absorbancy. However, the rate of enter the cells; five to eight volumes of cold 0.05 reduction of ketose is not constant. The rates M tris(hydroxymethyl)aminomethane acetate reported are linear estimates of the rates re- (tris acetate) buffer, pH 7.0, were discharged corded during the first minute of reaction. rapidly into the centrifuge tube as the contents The unit of enzymatic activity is defined as were stirred vigorously with a mechanical stirrer. the amount of enzyme which causes a change in The resulting viscous fluid was centrifuged at absorbancy at 340 m,u of 0.001 per min in the 10,000 to 15,000 X g for 10 min to remove standard assay with polyol. Specific activity is residual cells (less than 5% of the initial cells) defined as units of enzyme per mg protein as and the emptied cell envelopes. Centrifugation determined with the Folin-Ciocalteau reagent removes at least 90% of the reduced diphospho- (Lowry et al., 1951) using crystalline serum pyridine nucleotide (DPNH) oxidase which albumin as the standard. otherxxise would interfere with the dehydrogenase Substrates. Glycerol, erythritol, ribitol (ado- assay. The crude extract was stored at 0 to 4 C. nitol), D-arabitol, L-arabitol, xylitol, D-mannitol, Dehydrogenase assay. The assay measures the sorbitol (D-glucitol), galactitol (dulcitol), and rate of formation of DPNH subsequent to the D-rhamnitol were obtained from commercial addition of diphosphopyridine nucleotide (DPN) sources. Perseitol and L-iditol were gifts from to a buffered reaction mixture containing poly- C. E. Ballou, Department of Biochemistry, hydric alcohol and cell extract. The assay was University of California, Berkeley, Calif. D- made in the following manner. All solutions Xylulose was obtained from G. Ashwell of the except the enzyme preparation were made in the National Institutes of Health, Bethesda, Md. 226 MARCUS AND MARR [VOL. 82 TABLE 1. Utilization of various compounds as the was equilibrated with 0.05 M tris acetate, pH 7.0, sole carbon source by Azotobacter agilis before use. Growth No growth RESULTS D-Mannitol Galactitol Carbon source for growth. A. agilis grows well Sorbitol Ribitol in Burk's nitrogen-free basal medium containing D-Arabitol L-Arabitol a variety of polyols as the sole source of carbon. Xylitol Table 1 shows the polyols and a few related Erythritol compounds which support growth. Glycerol Induction of polyol dehydrogenases. The initial experiments on the specificity of induction by D-Fructose D-Mannose D-mannitol and sorbitol were misleading because L-Sorbose D-Ribose in both of Sucrose Lactose of impurities both polyols. Although D-Glucose these polyols were the best commercial prepara- tions available, with melting points identical One hundred milliliters of Burk's nitrogen-free with the accepted values, each was sufficiently basal medium, containing 0.1 M concentration of contaminated, presumably by the other, to the above compounds, was inoculated with 0.5 ml confuse the results of induction and assay. A. of an exponentially growing culture in Burk's agilis grown on either of the commercial polyols sucrose medium. Cultures were incubated on a as the sole carbon source gave extracts which rotary shaker at 30 C for 24 hr. oxidized both polyols (Table 2). However, the extracts of cells grown on commercial mannitol D-Ribulose was prepared by epimerization of oxidized mannitol more rapidly, and cells grown D-arabinose in dry pyridine (Glatthaar and on commercial sorbitol oxidized sorbitol more Reichstein, 1935). The o-nitrophenylhydrazone rapidly. These results suggested that different of D-ribulose was prepared and recrystallized quantities of two distinct polyol dehydrogenases from absolute ethanol (mp 167).
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