Quantitative measurement of the L-type pentose phosphate cycle with [2-14C]glucose and [5-14C]glucose in isolated hepatocytes

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Abstract
Investigations of the mechanism of the non-oxidative segment of the pentose phosphate cycle in isolated [rat] hepatocytes by prediction-labeling studies following the metabolism of [2-14C]-, [5-14C]- and [4,5,6-14C]glucose are reported. The 14C distribution patterns in G-6-P show that the reactions of the L-type pentose cycle are the exclusive form of the pentose pathway in hepatocytes. Estimates of the quantitative contribution of the L-type pentose cycle to glucose metabolism were made. The contribution of the L-type pentose cycle to the metabolism of glucose lies between 22 and 30% in isolated hepatocytes. The distribution of 14C in the C atoms of G-6-P following the metabolism of [4,5,6-14C]- and [2-14C]glucose indicate that gluconeogenesis from triose phosphate and non-oxidative formation of pentose 5-phosphate do not contribute significantly to randomization of 14C in isolated hepatocytes. The transaldolase [EC 2.2.1.2] exchange reaction between fructose 6-phosphate and glyceraldehyde 3-phosphate is very active in these cells.