New reaction sequences for the non-oxidative pentose phosphate pathway

Area of Science:

• Biochemistry
• Metabolic pathways
• Enzymology

Background:

• The non-oxidative pentose phosphate pathway is crucial for cellular metabolism.
• Understanding the complete metabolic fate of pentose phosphates is essential for comprehending cellular energy production and biosynthesis.

Purpose of the Study:

• To investigate the metabolic fate of ribose 5-phosphate in rat liver.
• To identify novel intermediates and reactions within the pentose phosphate pathway.
• To elucidate the role of D-arabinose 5-phosphate in liver metabolism.

Main Methods:

• Enzymatic assays using rat liver enzymes.
• Radiolabeling studies with [U-14C]ribose 5-phosphate.
• Carbon balance analysis of reaction components.
• Paper chromatography and enzymatic characterization of intermediates.

Main Results:

• No 14C-labeled volatile compounds were formed or fixed during hexose 6-phosphate synthesis from ribose 5-phosphate.
• Five new intermediates of pentose 5-phosphate metabolism were identified, including D-arabinose 5-phosphate.
• D-Arabinose 5-phosphate was utilized by rat liver enzymes to produce hexose 6-phosphate and triose phosphate.
• D-Arabinose 5-phosphate was reversibly converted to other pentose 5-phosphates via an enzyme tentatively named arabinose phosphate 2-epimerase.
• D-Arabinose 5-phosphate utilization was observed in various rat tissues at rates comparable to D-ribose 5-phosphate.

Conclusions:

• A new reaction sequence for the non-oxidative pentose phosphate pathway in liver is proposed.
• D-Arabinose 5-phosphate plays a significant role in hepatic carbohydrate metabolism.
• The findings expand the known metabolic network of pentose phosphate processing in mammals.