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Pentose phosphate pathway in rat colonic epithelium
R N Butler1, K K Arora, J G Collins
1Department of Gastroenterology, Queen Elizabeth Hospital, Woodville South, South Australia.
Biochemistry International
|October 1, 1990
Summary
Colonic cells utilize glucose extensively, primarily converting it to lactate. The F-type pentose pathway plays a minimal role in this glucose metabolism, with the L-type pathway contributing significantly to pentose phosphate formation.
Area of Science:
- Biochemistry
- Cell Biology
- Gastroenterology
Background:
- Colonic cells are highly proliferative, requiring substantial nucleotide synthesis.
- The pentose pathway is crucial for producing ribose-5-phosphate (ribose 5-P) for nucleic acids and NADPH for biosynthesis.
- Colonocytes exhibit high pentose pathway enzyme activity, particularly in non-oxidative reactions.
Purpose of the Study:
- To investigate the role and contribution of F-type and L-type pentose pathways in colonocyte glucose metabolism.
- To elucidate the mechanisms of pentose phosphate formation in the colon.
- To quantify the F-type pentose cycle's contribution to overall glucose utilization.
Main Methods:
- Assessment of qualitative presence of oxidative pentose pathway via C-1/C-6 ratio.
- Measurement of F-type and L-type pentose pathway enzyme activities in colonocyte cytosol.
- Quantification of F-type pentose cycle contribution using the specific yield method.
- Analysis of [1-13C] ribose 5-P dissimilation products using 13C NMR spectroscopy.
- Measurement of transketolase and transaldolase exchange reactions.
Main Results:
- Colonocytes exhibit high glucose utilization (7.1 ± 0.33 μmol min-1g-1 dry wt), with 79% converted to lactate.
- The F-type pentose cycle's contribution to colonocyte glucose metabolism is negligible (approx. 1.5%).
- 13C NMR data and exchange reaction measurements indicate that C-1/C-3 labeling in hexose phosphates is mainly due to transketolase/transaldolase activity, not the F-type pathway.
- Arabinose 5-P plays an intermediary role in converting ribose 5-P to hexose phosphates.
Conclusions:
- The F-type pentose pathway has a minimal role in colonocyte glucose metabolism.
- Pentose phosphate formation in colonocytes likely occurs predominantly via the L-type pathway, contributing approximately 20% of total glucose metabolism.
- Exchange reactions catalyzed by transketolase and transaldolase are significant in shaping the metabolic products of pentose phosphates in colonocytes.