VITAMIN E (TOCOPHEROL)

Vitamin E & lipoproteins

Vitamin E is primarily associated with the lipoprotein fraction of the plasma, and protects the lipids against peroxidation. It also accumulates in adipose tissue.

Figure
α-tocopherol in LDL particle

Oxidative stress and vitamins C and E

Oxygen is potentially toxic for living organisms. While it is great as an electron sink, in the presence of free radicals, it can form highly reactive, super-oxidizing molecules that destroy proteins, nucleic acids and lipids. Oxidative stress leads to accelerated aging in plants and animals. In humans it is associated with degenerative diseases.

In plants, systems have evolved that detoxify superoxides, using ascorbic acid (vitamin C) and α-tocopherol (vitamin E) as key components.

Humans cannot synthesize ascorbic acid or α-tocopherol and thus must obtain them in their diet. Hence, they are called vitamins.

The idea that antioxidants protect against aging and degenerative disease is still controversial, and will be discussed in later lectures.

Figure
Plant detoxification
One example of how vitamin C detoxifies superoxide in chloroplasts

See Halvorsen et al, J. Nutrition (2001) A systematic screening of total antioxidants in plants