Zinc Biosynthesis – Function and Metabolism

What Is Zinc Biosynthesis?

The term zinc biosynthesis refers, in a biological context, to the complete set of processes by which zinc is absorbed, transported, incorporated into proteins and enzymes, regulated, and eventually excreted in the human body. Since the human body cannot synthesize zinc on its own, it depends entirely on dietary intake. The biological availability and enzymatic incorporation of zinc into endogenous structures are therefore key aspects of zinc biosynthesis.

Biological Functions of Zinc

Zinc is involved in more than 300 enzymatic reactions and is considered one of the most important trace elements in the human body. It performs catalytic, structural, and regulatory roles:

• Catalytic role: Zinc is a component of many enzymes, including DNA polymerases, carbonic anhydrase, and alkaline phosphatase.
• Structural role: Zinc stabilizes the three-dimensional structure of proteins, such as zinc finger proteins involved in gene regulation.
• Regulatory role: Zinc influences cell signaling and plays a key role in immune system regulation.
• Antioxidant role: Zinc is a component of superoxide dismutase (SOD), protecting cells from oxidative stress.

Absorption and Transport of Zinc

Zinc is primarily absorbed in the small intestine, particularly in the jejunum. Specialized transport proteins -- known as ZIP transporters (Zrt- and Irt-like proteins) and ZnT transporters (zinc transporters) -- regulate the uptake of zinc into intestinal cells and its subsequent transport into the bloodstream and organs. In the blood, zinc is mainly transported bound to albumin and alpha-2-macroglobulin.

Incorporation of Zinc into Enzymes and Proteins

The incorporation of zinc into apoenzymes (inactive enzyme precursors) occurs intracellularly with the help of metallochaperone proteins, which deliver zinc specifically to target proteins. This process is essential for the activation of numerous enzymes and the maintenance of cellular homeostasis. Zinc finger proteins, which are involved in gene transcription, also bind zinc in a highly specific manner.

Regulation of Zinc Levels

The body maintains zinc homeostasis through several finely tuned mechanisms:

• Intestinal absorption: When zinc levels are low, absorption in the intestine is upregulated.
• Metallothioneins: These intracellular proteins bind zinc and serve as a storage and buffering system.
• Renal excretion: The kidneys adjust zinc excretion according to the body's needs.
• Hepcidin and related signaling molecules: Certain signaling pathways coordinate zinc regulation depending on inflammatory status and metabolic conditions.

Dietary Sources and Bioavailability

Zinc is found in both animal and plant-based foods, although its bioavailability varies considerably:

• Animal sources: Oysters, beef, poultry, seafood, and dairy products provide highly bioavailable zinc.
• Plant-based sources: Legumes, nuts, seeds, and whole grains contain zinc but also phytates, which can inhibit its absorption.

The World Health Organization (WHO) recommends a daily zinc intake of approximately 7 to 14 mg for adults, depending on age, sex, and dietary habits.

Zinc Deficiency and Toxicity

A zinc deficiency can lead to impaired immune function, growth retardation, skin changes, hair loss, and reduced sense of taste and smell. Particularly at-risk groups include pregnant and breastfeeding women, older adults, and individuals with malabsorption syndromes.

Excessive zinc intake, for example through high-dose supplements, can cause toxic effects including copper deficiency, nausea, and impaired immune function.

References

1. World Health Organization (WHO) - Trace Elements in Human Nutrition and Health. Geneva, 1996.
2. Maret W., Sandstead H.H. - Zinc requirements and the risks and benefits of zinc supplementation. Journal of Trace Elements in Medicine and Biology, 2006.
3. Cousins R.J. - Zinc. In: Modern Nutrition in Health and Disease. 11th ed. Lippincott Williams and Wilkins, 2014.