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The phosphogluconate pathway and synthesis of 5-phosphoribosyl-1-pyrophosphate in human fibroblasts
Abstract:
The phosphogluconate pathway (pentose phosphate cycle) of normal fibroblasts was stimulated 20-fold by methylene blue and inhibited to 14% of the baseline rate by 6-aminonicotinamide. In fibroblasts deficient in glucose-6-phosphate dehydrogenase activity (an average of 1.5% of normal mean), the pentose phosphate cycle was unaffected by either methylene blue or 6-aminonicotinamide. In normal cells, neither the intracellular concentration nor the rate of generation of 5-phosphoribosyl-1-pyrophosphate was altered by the marked and opposite changes in the rate of the phosphogluconate pathway caused by methylene blue and 6-aminonicotinamide. Intracellular ribose 5-phosphate concentration was increase by methylene blue (an average increase of 83%) but not significantly altered by 6-aminonicotinamide. In fibroblasts deficient in glucose-6-phosphate dehydrogenase activity, the 5-phosphoribosyl-1-pyrophosphate concentration and rate of generation were higher rather than lower in comparison to normal cells under all conditions studied. The data suggest a predominant role for the nonoxidative branch of the phosphogluconate pathway in supplying ribose 5-phosphate for nucleotide biosynthesis. Pentose phosphate supply cannot be considered an essential function of the oxidative branch in fibroblasts.
Insights
The nonoxidative branch of the phosphogluconate pathway (pentose phosphate cycle) is crucial for ribose 5-phosphate supply in fibroblasts. The oxidative branch
Area of Science:
- Biochemistry
- Cell Biology
- Metabolic Pathways
Background:
- The phosphogluconate pathway, also known as the pentose phosphate cycle, is vital for producing NADPH and pentose sugars.
- Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in the oxidative phase of this pathway.
Purpose of the Study:
- To investigate the role of the oxidative and nonoxidative branches of the phosphogluconate pathway in supplying ribose 5-phosphate for nucleotide biosynthesis in fibroblasts.
- To determine the impact of methylene blue and 6-aminonicotinamide on the pentose phosphate pathway and related metabolites.
Main Methods:
- Stimulation of the phosphogluconate pathway using methylene blue and inhibition using 6-aminonicotinamide in normal fibroblasts.
- Analysis of fibroblasts with deficient glucose-6-phosphate dehydrogenase activity.
- Measurement of intracellular concentrations and generation rates of 5-phosphoribosyl-1-pyrophosphate and ribose 5-phosphate.
Main Results:
- Methylene blue significantly increased pentose phosphate pathway activity and ribose 5-phosphate levels in normal cells.
- 6-aminonicotinamide inhibited the pathway, but did not significantly alter ribose 5-phosphate or 5-phosphoribosyl-1-pyrophosphate levels.
- Fibroblasts deficient in G6PD showed higher 5-phosphoribosyl-1-pyrophosphate concentrations and generation rates, with unaffected pentose phosphate pathway activity.
Conclusions:
- The nonoxidative branch of the phosphogluconate pathway plays a predominant role in supplying ribose 5-phosphate for nucleotide biosynthesis in fibroblasts.
- The oxidative branch of the pentose phosphate pathway is not essential for providing pentose phosphate in these cells.