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D-Fructose 6-Phosphate, to the Acceptor, Either D-Glyceraldehyde 3-Phosphate Or Downloaded by Guest on September 30, 2021 VOL

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D-Fructose 6-Phosphate, to the Acceptor, Either D-Glyceraldehyde 3-Phosphate Or Downloaded by Guest on September 30, 2021 VOL 1942 BIOCHEMISTRY: PONTREMOLI ET AL. PROC. N. A. S. * Aided by grants from the National Institute of Arthritis and Metabolic Diseases (Grant A-1845) of the U.S. Public Health Service, and the Rockefeller Foundation. 1 Abbreviations: RNA, ribonucleic acid; the capital letters A, U, and C are used for the nucleotides adenylic, uridylic, and cytidylic acid, respectively, or their corresponding residues in polynucleotide chains; ADP, UDP, and CDP, the 5'-diphosphates of adenosine, uridine, and cytidine; ATP and GTP, the 5'-triphosphates of adenosine and guanosine; Tris, tris(hydroxy- methyl)aminomethane. 2 Gamow, G., Nature, 173, 318 (1954). 3Crick, F. H. C., J. S. Griffith, and L. E. Orgel, these PROCEEDINGS, 43, 416 (1957). 4Ycas, M., Nature, 188, 209 (1960). 5 Woese, C. R., Biochem. Biophys. Res. Comm., 5, 88 (1961) 6 Sueoka, N., these PROCEEDINGS, 47, 1141 (1961). 7 Jacob, F., and J. Monod, J. Mol. Biol., 3, 318 (1961). 8 Brenner, S., F. Jacob, and M. Meselson, Nature, 190, 576 (1961). 9 Gros, F., H. Hiatt, W. Gilbert, C. G. Kurland, R. W. Risebrough, and J. D. Watson, Nature, 190, 581 (1961). 10 Grunberg-Manago, M., P. J. Ortiz, and S. Ochoa, Biochim. Biophys. Acta, 20, 269 (1956). 11 Nirenberg, M. W., and J. H. Matthaei, these PROCEEDINGS, 47, 1558 (1961). 12 Rendi, R., and T. Hultin, Expl. Cell Research, 19, 253 (1960). 13 Zamecnik, P. C., and E. B. Keller, J. Biol. Chem., 209, 337 (1954). 14 Hoagland, M. B., M. L. Stephenson, J. F. Scott, L. I. Hecht, and P. C. Zamecnik, J. Biol. Chem., 231, 241 (1958). 16 Gierer, A., and G. Schramm, Nature, 177, 702 (1956). 16 Lengyel, P., and R. W. Chambers, J. Am. Chem. Soc., 82, 752 (1960). 17 Lengyel, P., and C. Basilio, to be published. 18 Zamecnik, P. C.. R. B. Lotfield, M. L. Stephenson, and J. M. Steele, Cancer Research, 11, 592 (1951). 19 Lowry, 0. H., N. J. Rosebrough, A. L. Farr, and R. S. Randall, J. Biol. Chem., 193, 265 (1951). 20 Lengyel, P., and R. C. Warner, unpublished results. 21 A. Rich, personal communication. 22 A. Rich (personal communication) also observed no effect of this polymer. 23 Tsugita, A., and H. Fraenkel-Conrat, these PROCEEDINGS, 46, 636 (1960). 24 Yamazaki, H., and P. Kaesberg, Nature, 191, 97 (1961). THE PREPARATION OF CRYSTALLINE TRANSALDOLASE FROM CANDIDA UTILIS BY S. PONTREMOLI, B. D. PRANDINI,* A. BONSIGNORE, AND B. L. HORECKER THE INSTITUTE OF BIOLOGICAL CHEMISTRY, UNIVERSITY OF GENOA, GENOA, ITALY AND THE DEPARTMENT OF MICROBIOLOGY, NEW YORK UNIVERSITY SCHOOL OF MEDICINE Communicated October 23, 1961 Transaldolase was first isolated from brewer's yeast' and shown to catalyze the reversible reaction: Sedoheptulose 7-phosphate + D-glyceraldehyde 3-phosphate D-erythrose 4-phosphate + D-fructose 6-phosphate (1) In the course of the reaction a three- carbon unit equivalant to dihydroxyacetone is transferred from the donor, which may be either sedoheptulose 7-phosphate or D-fructose 6-phosphate, to the acceptor, either D-glyceraldehyde 3-phosphate or Downloaded by guest on September 30, 2021 VOL. 47, 1961 BIOCHEMISTRY: PONTREMOLI ET AL. 1943 D-erythrose 4-phosphate. During transfer the three-carbon group must be firmly bound to the enzyme, since free dihydroxyacetone itself does not act as a donor and since no reaction occurs in the absence of acceptor. Nor does the active group exchange appreciably with free dihydroxyacetone in the medium.' Other sub- stances will also act as acceptors in the transaldolase reaction. These include ribose 5-phosphate, which yields octulose phosphate,2 D-glyceraldehyde and L- glyceraldehyde 3-phosphate, which are converted to D-fructose3 and D-sorbose 6- phosphate respectively,4 formaldehyde, which yields erythrulose,4 D-erythrose, which yields sedoheptulose,5 and pyruvic aldehyde which yields 5-ketofructose.6 None of these acceptors is as active as D-glyceraldehyde 3-phosphate or D-erythrose 4-phosphate, which suggests that these compounds are the true acceptor substrates for the enzyme. The requirement for an acceptor for the active dihydroxyacetone group is no longer evident when transaldolase and transketolase act simultaneously with fructose 6-phosphate as the donor.7 8 In this case sedoheptulose 7-phosphate is apparently formed as a result of the following coupled reactions: D-Fructose 6-phosphate + transaldolase = D-glyceraldehyde 3-phosphate + transaldolase-dihydroxyacetone complex (2) D-Fructose 6-phosphate + transketolase =± D-erythrose 4-phosphate + trans- ketolase-glycolaldehyde complex (3) D-Erythrose 4-phosphate + tranisaldolase-dihydroxyacetone complex = sedoheptulose 7-phosphate + transaldolase (4) D-Glyceraldehyde 3-phosphate + transketolase-glycolaldehyde complex = D-xylulose 5-phosphate + transketolase (5) Sum: 2 D-fructose 6-phosphate = sedoheptulose 7-phosphate + D-xylulose 5-phosphate (6) The amount of each acceptor formed in reactions (2) and (3), either D-glycer- aldehyde 3-phosphate or D-erythrose 4-phosphate, is limited by the concentration of enzyme added. These concentrations (about 10-8M) are far too low to permit reactions (4) and (5) to proceed at measurable rates. Since the over-all reaction (6) does proceed without a lag, some other explanation must be sought. In order to provide further information on the nature of this reaction, it was desirable to obtain transaldolase in pure form and to study the nature of the linkage of dihydroxyacetone to the enzyme. We have now developed a procedure for the isolation of crystalline transaldolase from low-temperature-dried commercial preparations of Candida utilis. When stoichiometric amounts of crystalline enzyme are incubated with fructose 6-phosphate-i-C14, the protein becomes labeled. Such labeling of transaldolase was first attained by Venkataraman et al.9 who demonstrated a slow exchange of radio-active dihydroxyacetone and fructose 6- phosphate. More recently, these workers have described the preparation of crystalline transaldolase from baker's yeast and the formation of labeled trans- aldolase from radioactive fructose 6-phosphate.'0 Although our preparation from Candida has a considerably higher specific activity then that reported by Venk- ataraman and Racker,4 it becomes labeled to a similar extent. Some properties of the labeled enzyme complex are reported in the following paper." Downloaded by guest on September 30, 2021 1944 BIOCHEMISTRY: PONTREMOLI ET AL. PROC. N. A. S. Experimental Procedures.-Materials: Sedoheptulose 1,7-diphosphate was prepared from fructose 1,6-diphosphate and fructose 6-phosphate as previously described.12 Coenzymes were obtained from the Sigma Chemical Corporation. Fructose 6-phosphate was obtained from Boehringer und Soehne and purified when necessary by paper chromatography. Glucose 6- phosphate dehydrogenase, aldolase and a-glycerophosphate dehydrogenase containing triose phosphate isomerase were also obtained from Boehringer und Soehne. Either this product or the 50-70 ammonium sulfate fraction from rabbit muscle"3 served as a source of these enzymes for the transaldolase assay. D-Gluconate 6-phosphate dehydrogenase was a crystalline preparation from Candida utilis.'4 Candida utilis, dried at low temperature, was generously supplied by the Lake States Yeast Corporation of Rhinelander, Wisconsin. Calcium phosphate gel was prepared by the procedure of Keilin and Hartree."5 Glucose 6-phosphate-i-C'4 was purchased from the Picker Company. The radiochemical purity was checked in two ways. In paper chromatography with ethyl acetate-isopropanol as a solvent only a single spot was found to be present. The preparation was also tested for the loca- tion of the label by treating it with excess of TPN in the presence of glucose 6-phosphate de- hydrogenase and D-gluconate 6-phosphate dehydrogenase. This procedure converts glucose 6- phosphate to ribulose 5-phosphate and liberates the C-1 carbon as CO2. Following the reaction the solution was acidified and plated. Only 5 per cent of the count remained, indicating that at least 95 per cent of the radioactivity was present as glucose 6-phosphate-i-C'4. Fructose 6- phosphate-1-C'4 as a contaminant was excluded since both enzyme preparations are free of phosphohexose isomerase. Methods: Spectrophotometric measurements were made with the Optikon Spectrophotometer. Radioactivity was measured with a Nuclear-Chicago micromil window gas-flow counter. Correc- tions for self absorption were made by adding a standard C'4 solution in the solution to be counted and recounting it. Transketolase was determined as previously reported.'6 Ribose phosphate isomerase was measured by the procedure of Axelrod and Jang'7 and phosphohexose isomerase was assayed with fructose 6-phosphate, TPN, and glucose 6-phosphate dehydrogenase. Glucose 6-phosphate was analyzed with TPN and glucose 6-phosphate dehydrogenase and fructose 6-phosphate by the same procedure with phosphohexose isomerase added. Protein was determined spectrophotometrically by the method of Bucher." As a standard we used a thoroughly dialyzed solution of crystalline transaldolase, the protein concentration of which was determined by micro-Kjeldahl analysis.t Enzyme assay: In previous studies with transaldolasel the assay procedure was based on the formation of fructose 6-phosphate with sedoheptulose 7-phosphate and D-glyceraldehyde 3- phosphate as donor and acceptor substrates, respectively. Fructose 6-phosphate was converted to glucose 6-phosphate by hexose phosphate isomerase and coupled to TPN and glucose 6-phos- phate dehydrogenase. In the assay mixture D-glyceraldehyde 3-phosphate was generated from fructose 1,6-diphosphate
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