heme

This term refers specifically to the iron-binding prosthetic group found in proteins like hemoglobin and myoglobin. It is a technical biochemical term used primarily in medical, biological, and chemical contexts to describe the specific molecular structure that allows for oxygen transport and electron transfer.

As a specialized chemical entity, it is treated as an uncountable mass noun in most scientific descriptions. It does not typically take a plural form unless referring to different types of heme groups or specific chemical variations in a comparative study.