How do some mammals produce ascorbic acid, while others require a dietary supply of it, and what is the significance of this difference?

Sourav PanNovember 9, 2024

Answered

Some mammals can synthesize ascorbic acid (vitamin C) while others require it from dietary sources due to evolutionary changes that have affected the presence and function of the enzyme L-gulonolactone oxidase (GULO). Here’s a detailed explanation of this phenomenon, its causes, and its significance.

Synthesis of Ascorbic Acid

1. Pathway of Synthesis:
   • In mammals capable of synthesizing vitamin C, the process begins with glucose. The metabolic pathway converts glucose into L-gulono-1,4-lactone, which is then oxidized to ascorbic acid by the enzyme GULO. This enzyme is crucial for the final step of vitamin C synthesis and is typically found in the liver or kidneys of these animals.
2. Loss of GULO Function:
   • Certain species, including humans, nonhuman primates (like monkeys), guinea pigs, and some bats, have lost the ability to produce GULO due to mutations in the gene encoding this enzyme. This mutation prevents them from completing the synthesis pathway for ascorbic acid, making it essential for these animals to obtain vitamin C through their diet .

Consequences of Vitamin C Dependency

1. Nutritional Requirements:
   • For species that cannot synthesize vitamin C, dietary intake becomes crucial. These animals must consume fruits and vegetables rich in ascorbic acid to meet their physiological needs. A deficiency in vitamin C can lead to scurvy, characterized by symptoms such as fatigue, gum disease, and impaired wound healing.
2. Physiological Roles:
   • Ascorbic acid serves multiple functions in mammals, including acting as an antioxidant, a cofactor for enzymatic reactions (such as collagen synthesis), and a regulator of gene expression . The inability to synthesize it can impair these critical functions, leading to various health issues.

Significance of the Difference

1. Evolutionary Perspective:
   • The loss of GULO and subsequent dependence on dietary vitamin C likely reflects evolutionary adaptations to specific environmental conditions where dietary sources were readily available. This adaptation may have provided advantages in certain ecological niches but also imposed constraints on dietary habits .
2. Health Implications:
   • Understanding the differences in vitamin C synthesis among mammals has important implications for nutrition and health management. For instance, it highlights the need for specific dietary recommendations for populations that cannot synthesize ascorbic acid .
3. Comparative Physiology:
   • Studying these differences enhances our understanding of metabolic pathways across species and can inform research into genetic mutations and their effects on health. It also raises questions about how similar losses in other metabolic pathways might affect other species