Pyridoxine acts as a coenzyme in:

Pyridoxine, also known as vitamin B6, plays a crucial role as a coenzyme in various biochemical reactions in the body. Specifically, it acts as a coenzyme in deamination and transamination processes, which are essential for amino acid metabolism.

In deamination, the amino group from an amino acid is removed, transforming it into a corresponding keto acid. This process is vital for the body to utilize amino acids for energy or convert them into other compounds. Transamination involves the transfer of an amino group to a keto acid, forming new amino acids. These reactions are fundamental for the synthesis and breakdown of amino acids, helping to maintain nitrogen balance and support various metabolic pathways.

The other choices do not correctly reflect the primary functions of pyridoxine. Iron transfer, fat transfer through the lymphatic system, and osmotic pressure of body fluids involve other nutrients or mechanisms and are not directly associated with the role of pyridoxine as a coenzyme. Therefore, recognizing the specific role of pyridoxine in amino acid metabolism clarifies why it is accurately identified with deamination and transamination processes.