title: New reaction sequences for the non-oxidative pentose phosphate pathway.
abstract: 1. Reactions leading to the formation of 14C-labelled volatile compounds and compounds volatile under acid conditions were investigated in a system actively synthesizing hexose 6-phosphates from [U-14C]ribose 5-phosphate by reactions catalysed by enzymes prepared from acetone-dried powder of rat liver; no reactions involving 14C-labelled volatile compounds were detected. Similarly the fixation of 14C-labelled volatile compounds into hexose 6-phosphate could not be detected. 2. A complete carbon balance was made for the reactants, intermediates and products of the reactions involved in the conversion of ribose 5-phosphate into hexose 6-phosphate by enzymes of rat liver. Five additional intermediates of pentose 5-phosphate metabolism in liver were detected, namely D-manno-heptulose 7-phosphate, D-altro-heptulose 1,7-bisphosphate, D-glycero-D-ido-octulose 1,8-bisphosphate, D-glycero-D-altro-octulose 1,8-bisphosphate and D-arabinose 5-phosphate. 3. D-Arabinose 5-phosphate was found to be utilized by a rat liver enzyme preparation to produce both hexose 6-phosphate and triose phosphate. 4. D-Arabinose 5-phosphate was reversibly converted into other pentose 5-phosphates. Paper chromatographic and enzymic evidence indicated that the conversion involved an enzyme tentatively named arabinose phosphate 2-epimerase, which catalyses the following reaction: D-arabinose 5-P in equilibrium D-ribose-5-P. 5. A variety of rat tissues also utilized D-arabinose 5-phosphate to produce both hexose 6-phosphate and triose phosphate and at a rate comparable with that obtained with D-ribose 5-phosphate. 6. A new reaction sequence for the non-oxidative pentose phosphate pathway in liver is proposed.
mesh_terms: D000818:Animals; D001089:Arabinose; D055598:Chemical Phenomena; D002621:Chemistry; D002854:Chromatography, Paper; D006600:Hexosephosphates / Q000096:biosynthesis; D008099:Liver / Q000201:enzymology; D010428:Pentosephosphates / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism; D051381:Rats; D012267:Ribosemonophosphates / Q000378:metabolism; D014153:Transaldolase / Q000378:metabolism; D014306:Trioses
chemical_list: D006600:Hexosephosphates; D010428:Pentosephosphates; D012267:Ribosemonophosphates; D014306:Trioses; D001089:Arabinose; D014153:Transaldolase; D010770:Phosphotransferases