L–ysine is well known for its effects in controlling viral infections. 

Lysine can help correct the imbalances (excess dietary arginine) leading to herpes, the virus that can cause painful mouth sores and fever blisters.

Lysine is also required for adequate absorption of calcium and for collagen formation (a vitamin C dependent process).

Lysine can enter metabolic pathways that eventually provide necessary ingredients for the production of energy.

This is true of many of the amino acids and is the reason protein can be a source of energy (kcals).