Vol. 83 AMINO ACIDS IN INTESTINE AND PORTAL PLASMA 135 TEvans, R. J. & McGinnis, J. (1948). J. Nutr. 85, 477. Kamin, H. & Handler, P. (1952). Amer. J. Phy8iol. 169, Geiger, E., Courtney, G. W. & Geiger, L. E. (1952). Arch. 305. Biochem. Biophy8. 41, 74. Kratzer, F. H. (1944). J. biol. Chem. 153, 237. Gibson, Q. H. & Wiseman, G. (1951). Biochem. J. 48, Naet, E. S. (1957). J. Amer. med. A88. 184, 172. 426. Nasset, E. S., Schwartz, P. & Weiss, H. V. (1955). J. Guggenheim, K., Halevy, S. & Friedmann, N. (1960). Nutr. 56, 83. Arch. Biochem. Biophy8. 91, 6. Pinsky, J. & Geiger, E. (1952). Proc. Soc. exp. Biol., N. Y., Gupta, J. D., Dakroury, A. M. & Harper, A. E. (1958). 81, 55. J. Nutr. 64, 447. Riesen, W. H., Clandinin, D. R., Elvehjem, C. A. & Hagihara, H., Ogata, M., Takedatsu, N. & Suda, M. (1960). Cravens, W. W. (1947). J. biol. Chem. 167, 143. J. Biochem., Tokyo, 47, 139. Rogers, Q. R., Chen, M. L., Peraino, C. & Harper, A. E. Hoeber, R. & Hoeber, J. (1937). J. ceU. comp. Phy8iol. 10, (1960). J. Nutr. 72, 331. 401. Sheffner, A., Adachi, R. & Spector, H. (1956). J. Nutr. 60, Hou, H. C., Riesen, W. H. & Elvehjem, C. A. (1949). Proc. 507. Soc. exp. Biol., N. Y., 70, 416. Waterlow, J. C. & Stephen, J. M. L. (1957). In Proc. ConJ Jacquot, R., Matet, J. & Fridensen, 0. (1947). Ann. Nutr., Human Protein Requirements and their Fulfllment in Pari8, 1, 157. Practice, Princeton, U.S.A., 1955, p. 145. Biochem. J. (1962) 83, 135 Polyol Dehydrogenases 4. CRYSTALLIZATION OF THE L-IDITOL DEHYDROGENASE OF SHEEP LIVER* BY M. G. SMITHt Department of Biochemi8try, Medical School, University of Otago, Dunedin, New Zealand (Received 31 August 1961) L-Iditol dehydrogenase (sorbitol dehydrogenase) 1959) and guinea-pig-liver mitochondria (Holl- operates specifically with DPN and catalyses the mann & Touster, 1957). The partially purified reversible oxidation of several acyclic polyols to enzyme extracted from guinea-pig-liver mito- ketoses (Blakley, 1951). Fully hydroxylated chondria (Hollmann, 1959) has been called 'DPN- pentitols, hexitols and heptitols are oxidized if xylitol (D-xylulose) dehydrogenase' (Hickman & they possess configuration (I) or (II) (McCorkindale Ashwell, 1959). & Edson, 1954), C* indicating the site of oxidation. McCorkindale & Edson (1954) showed that sub- strates of L-iditol dehydrogenase possessing con- CH2.OH CH2. OH figuration (I) (sorbitol, L-iditOl, xylitol) are oxi- *-OH H__C*-.jOH dized substantially faster than those with con- figuration (II) (allitol, ribitol). It is possible that HO-1H H--GOH their rat-liver preparation contained two polyol H-C-OH H-C-OH dehydrogenases, each specific for one of these con- figurations, but the data of Williams-Ashman et al. (1957) provide evidence that a single enzyme is (I) (II) responsible for the oxidation of both types of The enzyme occurs in the livers of all mammalian polyol. species that have been examined and procedures To apply a more exacting test to the unitary have been described for significant purification of hypothesis, an extensive purification of the readily the enzyme from some species (Williams-Ashman & extractable polyol dehydrogenase of sheep liver Banks, 1954; Todd, 1954; King & Mann, 1959; was undertaken. A preliminary note on the crystal- Holzer & Goedde, 1960). Similar enzymic activity lization of the enzyme has been published (Smith, has been found in certain male accessory sexual 1960). glands (Williams-Ashman, Banks & Wolfson, MATERIALS AND METHODS 1957; Hers, 1957), spermatozoa (King & Mann, Materia8 * Part 3: Shaw (1956). Source of the enzyme. Sheep livers were obtained at the t Present address: Department of Biochemistry, slaughter-house within 15 min. of the death of the animals University of Oxford. and immediately chilled in crushed ice. Livers of starved 136 M. G. SMITH 1962 pregnant or lactating sheep were unsatisfactory because of specific activity of enzyme preparations is defined as the their high lipid content. number of enzyme units/mg. of protein. AmmoniuM sulphate. The amount of ammonium sulphate TPN-xylitol (L-xylulose) dehydrogenase was assayed by required to reach a desired percentage saturation was cal- the method of Hollmann (1959), aldolase by the method of culated from the Table of Green & Hughes (1955). For Peanasky & Lardy (1958), D-3-phosphoglyceraldehyde the purpose of calculation all solutions were assumed to be dehydrogenase by the method of Velick (1955) except that at room temperature. D-3-phosphoglyceraldehyde was formed in the cuvette by Alumina-Cv gel. This was prepared by the method of the action of aldolase on fructose 1,6-diphosphate, and Willstiitter & Kraut (1923). alcohol dehydrogenase by the method of Theorell & Organic solvents. Ethanol and acetone were distilled Bonnichsen (1951). from commercial materials. Measurement of pH. This was carried out by means of a Polyols. Xylitol was a product of the California Corp. glass electrode with a Marconi Instruments pH meter. for Biochemical Research, Los Angeles, Calif., U.S.A., and Measurement of extinction. This was done in a Beckman erythritol was obtained from Hopkin and Williams Ltd., DU spectrophotometer. The reaction mixtures were con- Chadwell Heath, Essex. The sources of the other polyols tained in silica cuvettes having a 1 cm. light path. have been reported earlier (McCorkindale & Edson, 1954; Protein estimation. Protein was estimated by the method Shaw, 1956). ofLowry, Rosebrough, Farr & Randall (1951). The standard Pentuloses. D-Xylulose was prepared according to curve was obtained with crystalline bovine plasma Levene & Tipson (1936) by Dr R. G. Kulka. L-Ribulose albumin (Armour Laboratories, Chicago, Ill., U.S.A.). and L-xylulose were prepared from L-arabinose and L- Pentulose estimation. Ribulose and xylulose were esti- xylose respectively by epimerization in pyridine (Glatthaar mated by the cysteine-carbazole reaction (Dische & & Reichstein, 1938). As much as possible of the unchanged Borenfreund, 1951) and identified by the absorption pentose was crystallized and removed. The syrup con- spectrum obtained in the orcinol-ferric chloride method taining L-ribulose was treated with bromine (Hudson & (Horecker, Smyrniotis & Seegmiller, 1951). Isbell, 1929) and the aldonic acids and salts were removed Ultracentrifugal analysis. This was done in a Spinco by ion-exchange on Amberlite IRA-400 (HC03- form) and model E ultracentrifuge with a 12-0 mm. standard cell. Amberlite IR-120 (H+ form). The product contained mainly Sedimentation coefficients were determined by measuring L-ribulose but paper chromatography (phenol-water) the distance moved by the maximum ordinate of the revealed the presence of small amounts of aldoses and gradient curve with a travelling microscope. The area under xylulose. A sample of the syrup containing L-xylulose was the curve was measured by projection of the plates and use purified by chromatography on a column (12 cm. x 0-2 cm.2) of a planimeter. The reference base-line was obtained ofDowex 1 (borate form) (Khym & Zill, 1952). Immediately according to Cecil & Ogston (1948). after elution the fractions containing L-xylulose were mixed with Amberlite IR-120 (H+ form) and the boric acid Purification of the enzyme was removed as volatile methyl borate (Zill, Khym & All operations were performed at 2° unless stated other- Cheniae, 1953). The product was free from aldoses, ribulose wise. and borate. Extraction. Finely minced sheep liver (2 kg.) was mixed Lactic dehydrogenase. Crystalline lactic dehydrogenase with 41. of 0 02M-phosphate buffer, pH 7-2, and allowed to (muscle) was obtained from the Sigma Chemical Co., St stand for 1 hr. with occasional stirring. The extract was Louis, Mo., U.S.A. filtered through a double layer of cheese-cloth. The specific Buffer solutions. Phosphate buffers were prepared from activity of the extract was 0-03-0 04 enzyme unit/mg. of solutions of disodium hydrogen phosphate and potassium protein. dihydrogen phosphate. Acetate buffers were prepared from Heat treatment of the extract. Samples (2 1.) of the crude acetic acid and sodium acetate. Glycine buffers were pre- extract contained in 6 1. flasks were heated to 570 in a pared by adjusting the pH of a solution of glycine with water bath at 650. The extract was agitated at 570 for sodium hydroxide. 8 min. and then cooled to 100 in an ice bath. The turbid Water. Water used in the enzyme purification was solutions were combined and centrifuged at 3000g for distilled twice in glass apparatus. 10 min. at 5-10°. The clear-red supernatant (specific activity 0 07-0 09 enzyme unit/mg. of protein) was kept Analytical methods and the copious precipitate of denatured protein discarded. Enzyme assays. The assay of L-iditol dehydrogenase About 70% of the enzyme originally in the extract was employed the DPN-linked oxidation of sorbitol to fructose. recovered. The experimental and reference cuvettes each contained Ammonium s8lphate fractionation at 100. Finely ground 120,moles of sorbitol, 65,umoles of glycine buffer, pH 9-6, ammonium sulphate was slowly added to the mechanically and approx. 01 unit of enzyme, in a final volume of stirred solution (initially at pH 7 0) until 45% saturation 2-4 ml. The reaction was started by adding 1 2 pemoles of was attained. The solution was allowed to stand for 1 hr. DPN to the experimental cuvette and the extinction, E, before it was centrifuged at 3000g. The precipitate was at 340 mte was read at 30 sec. intervals for 3 min. The initial discarded and the supernatant made 65% saturated with velocity was determined from the graph ofE340 against time. ammonium sulphate. The solution was allowed to stand for The relation between enzyme concentration and initial 1 hr. and then the precipitate was collected by centrifuging velocity was linear. The unit of enzymic activity is defined at 3000g, dissolved in 150-200 ml. of water and dialysed as the amount of enzyme which reduces 1 jumole of DPN/ against 10 1.