252 GERTRUDE E. GLOCK 



and leaves.^* The C2 fragment, which is not free glycolaldehyde/^ '^^"^^ has 

 not, however, been characterized. It may be glycolaldehyde in a "bound "^^ 

 or "active"" form which can also apparently arise enzymically from 

 dihydroxymaleic acid or hydroxypyruvic acid.^* Evidence has been ob- 

 tained with both yeast^^ and liver^^ enzymes that ribulose-5-phosphate and 

 not ribose-5-phosphate is the true substrate for the pentose phosphate- 

 splitting enzyme, since crude enzyme preparations attack both substrates 

 readily whereas partially purified preparations, although still containing 

 some pentose phosphate isomerase, attack ribulose-5-phosphate much more 

 readily than the ribose ester. Racker et al.^'' have recently isolated a crys- 

 talline enzyme, free from pentose phosphate isomerase, from baker's yeast 

 which catalyzes the cleavage of ribulose-5-phosphate with the formation 

 of D-glyceraldehyde-3-phosphate, which was identified. This cleavage only 

 occurs on the addition of an "acceptor aldehyde" such as ribose-5-phos- 

 phosphate or glycolaldehyde. 



b. Synthesis of Sedoheptulose-7 -phosphate and Hexosemonophosphate 



Degradation of pentose phosphate by blood hsemolysates,^" ■^'^ •''' partially 

 purified enzyme preparations from hver-^'^^'^^ and bone marrow, ^^ and by 

 many other mammalian tissues and tumors^- is accompanied by the forma- 

 tion of hexosemonophosphate. This synthesis of hexosemonophosphate has 

 been shown to proceed without passing through the intermediate stage of 

 fructose diphosphate.^"'^^ Dische-* and Glock,-^ using, respectively, blood 

 haemolysates and partially purified liver preparations, obtained approxi- 

 mately 75 % conversion of the ribose-5-phosphate that was degraded into 

 hexosemonophosphate. This is considerably in excess of the hexosemono- 

 phosphate which could be derived solely from the triose fragment of the 

 pentose phosphate. Evidence was also obtained that fructose monophos- 

 phate (presumably fructose-6-phosphate) was formed first and then grad- 

 ually converted into glucose-6-phosphate by the action of hexose phosphate 

 isomerase. Sedoheptulose monophosphate was soon detected as an inter- 



2'* Z. Dische, in "Phosphorus Metabolism" (McP-^hoy and Glass, eds.), Vol. 1, p. 



171. Johns Hopkins Press, Baltimore, 1951. 

 26 G. De la Haba and E. Racker, Federation Proc. 11, 201, (1952). 



26 B. L. Horecker, J. Cellular Camp. Physiul. 41, Suppl.l, 137 (1953). 



27 E. Racker, G. De la Haba, and I. G. Leder, J. Am.. Chem. Soc. 75, 1010 (1953). 



28 S. Akabori, K. Uehara, and I. Miramatsu, Proc. Japan Acad. 28, 39 (1952). 



29 B. L. Horecker and P. Z. Smyrniotis, Federation Proc. 11, 232 (1952). 



'" Z. Dische, Abstr. 1st Intern. Congr. Biochem., Cambridge p. 572 (1949). 



31 M. J. Waldvogel and F. Schlenk, Arch. Biochem. 14, 484 (1947); 22, 185 (1949). 



'2 Gertrude E. Glock and P. McLean, Biochem. J. 56, 171 (1954). 



33 F. Dickens and Gertrude E. Glock, Biochem. J. 50, 81 (1951). 



