L-gulono-γ-lactone oxidase expression and vitamin C synthesis in the brain and kidney of the African lungfish, Protopterus annectens.

This study aimed to test the hypothesis that the brain of Protopterus annectens expressed L-gulono-γ-lactone oxidase (gulo/Gulo), the enzyme catalyzing the last step of ascorbate biosynthesis, and could maintain high concentrations of ascorbate during estivation. We cloned and sequenced gulo from the kidney of P. annectens and performed quantitative PCR to determine its mRNA expression in kidney and brain. Gulo activity was assayed and its protein abundance was determined by Western blot using custom-made anti-Gulo antibody. Effects of estivation on concentrations of ascorbate and dehydroascorbate in the kidney and brain were also determined. Both brain and kidney, but not liver, of P. annectens expressed gulo/Gulo. Desiccation induced P. annectens to estivate, and 6 mo of estivation led to drastic decreases in gulo/Gulo expression and ascorbate concentration in the kidney. However, high concentrations of ascorbate and ascorbate + dehydroascorbate were maintained in the brain during estivation, probably resulting from in situ ascorbate synthesis. Control fish were placed in freshwater, where they were fully active in a favorable environment unlike estivation on land. The ability to synthesize ascorbate to ameliorate oxidative stress directly in the brain might contribute to the ability of P. annectens to undergo prolonged estivation on land.

The transcription of l-gulono-gamma-lactone oxidase, a key enzyme for biosynthesis of ascorbate, during development of Persian sturgeon Acipenser persicus.

l-Gulono-gamma-lactone oxidase (GULO) is a key enzyme for the biosynthesis of ascorbate, which is essential for several cellular functions. In the present study, mRNA expression of GULO gene was evaluated during the early development of Persian sturgeon. First, because there are no comparative studies that have established suitable quantitative real-time PCR reference genes in sturgeons for any physiological conditions, we evaluated six candidate reference genes (ACTB, RPL13, UBQ, RPL6, GAPDH and EF1A) during the early development of Persian sturgeon. The most stable mRNA expression was obtained with RPL6 and ACTB, whereas the least stable was RPL13. After normalization using RPL6, ACTB and RPL6/ACTB combination, the mRNA expression of GULO was highest at the embryonic stage (2days before hatching; P<0.05) and started to decline from hatching of larvae to the rest of the developmental time-points. This suggests that the vitamin C requirements are highest during early life stages, and it is likely that the changes in GULO mRNA expression are associated with changes in GULO enzyme activity.