Incapability of L-ascorbic acid synthesis by insects

Ascorbic acid biosynthesis in Pacific abalone Haliotis discus hannai Ino and L-gulonolactone oxidase gene loss as an independent event

Up to now, it has been believed that invertebrates are unable to synthesize ascorbic acid (AA) in vivo. However, in the present study, the full-length CDs (Coding sequence) of L-gulonolactone oxidase (GLO) from Pacific abalone (Haliotis discus hannai Ino) were obtained through molecular cloning. The Pacific abalone GLO contained a FAD-binding domain in the N-termination, and ALO domain and conserved HWAK motif in the C-termination. The GLO gene possesses 12 exons and 11 introns. The Pacific abalone GLO was expressed in various tissues, including the kidney, digestive gland, gill, intestine, muscle and mantle. The GLO activity assay revealed that GLO activity was only detected in the kidney of Pacific abalone. After a 100-day feeding trial, dietary AA levels did not significantly affect the survival, weight gain, daily increment in shell length, and feed conversion ratio of Pacific abalone. The expression of GLO in the kidney was downregulated by dietary AA. These results implied that the ability to synthesize AA in abalone had not been lost. From the evolutionary perspective, the loss of GLO occurred independently as an independent event by matching with the genomes of various species. The positive selection analysis revealed that the GLO gene underwent purifying selective pressure during its evolution. In conclusion, the present study provided direct evidence to prove that the GLO activity and the ability to synthesize AA exist in abalone. The AA synthesis ability in vertebrates might have originated from invertebrates dating back 930.31 million years.

The invertebrate Caenorhabditis elegans biosynthesizes ascorbate

L-ascorbate, commonly known as vitamin C, serves as an antioxidant and cofactor essential for many biological processes. Distinct ascorbate biosynthetic pathways have been established for animals and plants, but little is known about the presence or synthesis of this molecule in invertebrate species. We have investigated ascorbate metabolism in the nematode Caenorhabditis elegans, where this molecule would be expected to play roles in oxidative stress resistance and as cofactor in collagen and neurotransmitter synthesis. Using high-performance liquid chromatography and gas-chromatography mass spectrometry, we determined that ascorbate is present at low amounts in the egg stage, L1 larvae, and mixed animal populations, with the egg stage containing the highest concentrations. Incubating C. elegans with precursor molecules necessary for ascorbate synthesis in plants and animals did not significantly alter ascorbate levels. Furthermore, bioinformatic analyses did not support the presence in C. elegans of either the plant or the animal biosynthetic pathway. However, we observed the complete ¹³C-labeling of ascorbate when C. elegans was grown with ¹³C-labeled Escherichia coli as a food source. These results support the hypothesis that ascorbate biosynthesis in invertebrates may proceed by a novel pathway and lay the foundation for a broader understanding of its biological role.

Senescence Marker Protein 30: Functional and Structural Insights to its Unknown Physiological Function

Senescence marker protein 30 (SMP30) is a multifunctional protein involved in cellular Ca(2+) homeostasis and the biosynthesis of ascorbate in non-primate mammals. The primary structure of the protein is highly conserved among vertebrates, suggesting the existence of a significant physiological function common to all mammals, including primates. Enzymatic activities of SMP30 include aldonolactone and organophosphate hydrolysis. Protective effects against apoptosis and oxidative stress have been reported. X-ray crystallography revealed that SMP30 is a six-bladed β-propeller with structural similarity to paraoxonase 1, another protein with lactonase and organophosphate hydrolase activities. SMP30 has recently been tied to several physiological conditions including osteoporosis, liver fibrosis, diabetes, and cancer. This review aims to describe the recent advances made toward understanding the connection between molecular structure, enzymatic activity and physiological function of this highly conserved, multifaceted protein.

Ascorbate metabolism and its regulation in animals

This article provides a comprehensive review on ascorbate metabolism in animal cells, especially in hepatocytes. The authors deal with the synthesis and the breakdown of ascorbate as a part of the antioxidant and carbohydrate metabolism. Hepatocellular and interorgan cycles with the participation of ascorbate are proposed, based on experiments with murine and human cells; reactions of hexuronic acid pathway, non-oxidative branch of the pentose phosphate cycle, glycolysis and gluconeogenesis are involved. Besides the well-known redox coupling between the two major water-soluble antioxidants (glutathione and ascorbate), their metabolic links have been also outlined. Glycogenolysis as a major source of UDP-glucuronic acid determines the rate of hexuronic acid pathway leading to ascorbate synthesis. Glycogenolysis is regulated by oxidized and reduced glutathione; therefore, glycogen, ascorbate and glutathione metabolism are related to each other. Hydrogen peroxide formation, due to the activity of gulonolactone oxidase catalyzing the last step of ascorbate synthesis, also affects the antioxidant status in hepatocytes. Based on new observations a complex metabolic regulation is supposed. Its element might be present also in humans who lost gulonolactone oxidase but they need and metabolize ascorbate. Finally, the obvious disadvantages and the possible advantages of the lost ascorbate synthesizing ability in humans are considered.

Ascorbic acid in Drosophila and changes during aging

The ascorbic acid content of Drosophila melanogaster was found to be high in the absence of a dietary source. The amount of ascorbic acid per fly declined with aging in both the Oregon R and Swedish C strains. The median life span at 25 degrees C was 45 days for Swedish C and 59 days for Oregon R. The amount of ascorbic acid in Swedish C flies (0.078 micrograms/fly) was higher than that for Oregon R (0.058 micrograms/fly) for newly emerged flies but the rate of decline with aging was greater for Swedish C than Oregon R. The decline in ascorbic acid content with aging was 70.4% for Swedish C versus 19.9% for Oregon R. A brief cold shock was found to significantly increase the amount of ascorbic acid in Oregon R flies. Feeding the precursor of ascorbic acid synthesis, L-gulonolactone, did not improve the life span. Life-time feeding of ascorbic acid did not improve the life span of either Swedish C or Oregon R flies.

Vitamin C biosynthesis in prosimians: evidence for the anthropoid affinity of Tarsius

This report examines the taxonomic distribution of the in vitro biosynthesis of ascorbic acid in the Prosimii (Order: Primates). Liver and kidney samples of 15 prosimian taxa, including Tarsius bancanus, were quantitatively tested for the enzyme L-gulono-1,4-lactone oxidase. Liver samples from all taxa except Tarsius had substantial levels of the enzyme. Furthermore, unlike other eutherian mammals, kidney tissue from members of the family Lemuridae showed low but consistent levels of enzyme activity. The result for Tarsius, by fitting with the pattern exhibited by the monkeys, apes, and man, adds significant independent evidence for this animal's relatively close genetic relationship with the Anthropoidea.

Evolution and the biosynthesis of ascorbic acid

The ability to synthesize ascorbic acid is absent in the insects, invertebrates, and fishes. The biosynthetic capacity started in the kidney of amphibians, resided in the kidney of reptiles, became transferred to the liver of mammals, and finally disappeared from the guinea pig, the flying mammals, monkey, and man. A similar transition in the biosynthetic ability was observed in the branched evolution of the birds.