This heme is a large molecule that’s made up of four pyrrole subunits that forms a ring, and this structure is called a porphyrin.

血红大分子，由四吡咯基形成环形，这结卟啉。

This heme is a large molecule that's made up of four pyrrole subunits that form a ring, and this structure is called a porphyrin.

血红一由4吡咯基形成的环状大分子，这种结称之为卟啉。