Ribitol and flavinogenesis in Eremothecium ashbyii

Area of Science:

• Microbiology
• Biochemistry
• Enzymology

Background:

• Riboflavin (Vitamin B2) is essential for numerous metabolic processes.
• Eremothecium ashbyii is a known producer of riboflavin.
• Understanding the biosynthesis pathway is crucial for optimizing production.

Purpose of the Study:

• To investigate the effect of ribitol supplementation on riboflavin production in E. ashbyii.
• To identify and characterize enzymes involved in the riboflavin biosynthesis pathway.
• To elucidate the role of purines in enzyme activation and riboflavin formation.

Main Methods:

• Culturing E. ashbyii with various supplements, including ribitol, ribose, and ribulose phosphate.
• Enzyme assays using cell-free extracts to detect ribitol kinase, d-ribose reductase, d-ribose 5'-phosphatase, and GMP nucleosidase.
• Radioisotope labeling ([1-(14)C]ribose and [U-(14)C]GMP) to trace metabolic pathways.

Main Results:

• Ribitol supplementation increased riboflavin formation twofold compared to controls.
• Ribitol is preferentially incorporated over ribose into riboflavin.
• Enzymes involved in riboflavin synthesis were identified, with ribitol inducing ribitol kinase.
• Flavinogenic purines (guanine, xanthine) activated ribitol kinase in vitro.
• [U-(14)C]GMP was incorporated into riboflavin and a blue fluorescent intermediate.

Conclusions:

• Ribitol is a key precursor for enhanced riboflavin biosynthesis in E. ashbyii.
• The study identified critical enzymes and regulatory mechanisms in the riboflavin pathway.
• Purine activation of enzymes plays a significant role in optimizing riboflavin production.