L-lysine is an essential amino acid that is a necessary building block for all protein in the body. L-Proline is a major amino acid found in cartilage and is important for maintaining youthful skin, proper functioning of joints and tendons and helping to maintain and strengthen the heart muscle. Without adequate protein, your body cannot build the structures that make up your cells, tissues and organs, nor can it generate the biochemical substances it needs for cardiovascular function, muscle contraction and immune support.