Mechanism and contribution of the pentose phosphate cycle to glucose metabolism in epididymal fat tissue

Abstract

1. 1. Glucose 6-phosphate, fructose 6-phosphate and alfroheptulose 7-phosphate are the major products formed non-oxidatively from ribose 5-phosphate by rat epididymal fat pad enzymes. 2. 2. Arabinose 5-phosphate was detected among the reaction products and significant activity of the new enzyme of the L-type pentose pathway, d-glycero d-ido octulose 1,8-bisphosphate: d- altroheptulose 7-phosphotransferase was found. 3. 3. The glucose moieties of glucose 1-phosphate, glucose 6-phosphate and glucose 1,6-bisphosphate were degraded and showed that epididymal fat pad enzymes relocate 14C from [2- 14C] glucose into C-l, C-2 and C-3 of each hexose-phosphate. 4. 4. The 14-distribution patterns in the hexose-phosphates revealed that these intermediates were not in isotopic equilibrium and the rate of the transaldolase exchange reaction was relatively small. 5. 5. The 14C-distribution data suggest that glucose 1-phosphate, rather than glucose 6-phosphate, is the first intermediate in the path of glycogen synthesis from glucose in this tissue. 6. 6. The data provide the first proof of the mechanism of the pentose pathway in adipose tissue.