Magnesium is a component part of

Magnesium is a part of Chlorophyll.
The presence of magnesium in chlorophyll was discovered in 1906, and was that element's first detection in living tissue.
The chlorophyll molecule consists of a central magnesium atom surrounded by a nitrogen-containing structure called a porphyrin ring; attached to the ring is a long carbon-hydrogen side chain, known as a phytol chain.