250 GERTRUDE E. GLOCK 



phosphates and pentoses being detected by paper chromatography and 

 ribose and arabinose determined quantitatively by the use of pentose 

 adapted E. coli}^ Both D-ribose and D-arabinose were detected and ac- 

 counted for 25% and 10%, respectively, of the total apparent pentose 

 present. Of the pentose phosphates, two behaved like ribose-5-phosphate 

 and arabinose-5-phosphate but most was in the form of an unknown pen- 

 tose phosphate with a characteristic peak at 450 m/x in the Bial reaction. 

 This was considered to be a 1 , 2-enediol pentose-5-phosphate and was sug- 

 gested as the primary decarboxylation product of 6-phosphogluconate. 

 Recently, however, Cohen has shown that this unknown pentose phosphate 

 is probably an alkaline degradation product of ribulose-5-phosphate." The 

 following pentose phosphate interrelationships were suggested i^^ 



D-arabinose-5-phosphate ;^ D-ribulose-5-phosphate ^ D-ribose-5-phosphate 



h. Ribulose-5-phosphate 



The nature of the intermediates in 6-phosphogluconate oxidation has 

 also been investigated by Horecker and his co-workers'^ '^^ using a purified 

 yeast dehydrogenase preparation.^'^ In order to accumulate the oxidation 

 product without adding stoichiometric quantities of TPN, reoxidation of 

 reduced coenzyme was effected by adding an excess of pyruvate and lactic 

 dehydrogenase. By this means 6-phosphogluconate was oxidized quanti- 

 tatively to pentose phosphate with catalytic amounts of TPN: 



(1) 6-phosphogluconate + TPN+ -> pentose-5-phosphate + CO2 + TPNH + H+ 



(2) pyruvate + TPNH + H+ -^ lactate -f TPN+ 



Two pentose phosphates were detected which were separated by ion- 

 exchange chromatography on Dowex 1 formate. One phosphate was dextro- 

 rotatory and the other laevorotatory, the proportion of each component 

 depending on the time of incubation. The dextrorotatory compound was 

 identified by chromatographic and chemical methods as D-ribose-5-phos- 

 phate, the nature of the pentose being confirmed by the preparation of the 

 benzylphenylhydrazone. The laevorotatory compound was obviously a pre- 

 cursor of ribose-5-phosphate since it was the major component early in the 

 reaction but was gradually replaced by ribose-5-phosphate as the incuba- 

 tion proceeded. The pentose of this component was identified as D-ribulose 

 by means of its o-nitrophenylhydrazone, and on the basis of its conversion 

 to ribose-5-phosphate was presumed to be ribulose-5-phosphate. An equi- 

 ps S. S. Cohen and R. Raff, /. Biol. Chem. 188, 501 (1951). 

 " S. S. Cohen, /. Biol. Chem. 201, 71 (1953). 



15 B. L. Horecker and P. Z. Smyrniotis, Arch. Biochem. 29, 232 (1950). 



16 B. L. Horecker, P. Z. Smyrniotis, and J. E. Seegmiller, /. Biol. Chem. 193, 383 

 (1951). 



" B. L. Horecker and P. Z. Smyrniotis, J. Biol. Chem. 193, 371 (1951). 



