Pronunciation: [hˈiːm] (IPA) 
The spelling of the word "haem" is often confusing as some people use "hem" instead. However, the correct spelling of this word is "haem" and it refers to a constituent of blood. The spelling is derived from the Greek word "haima" and it is pronounced /hɛm/. The use of the "a" in the spelling is due to the influence of British English where it is traditionally spelled this way. In American English, it is spelled "hem" without the "a".
Haem, also commonly spelled as heme, is a complex organic molecule that plays a crucial role in the function of hemoglobin, myoglobin, and various enzymes in living organisms. It is a porphyrin derivative consisting of a flat, cyclic structure containing a central iron ion coordinated with a nitrogen atom. Haem is responsible for the binding and transport of oxygen in the bloodstream.
In the context of hemoglobin, haem forms the core of the protein and binds to oxygen molecules within red blood cells. This enables the transportation of oxygen from the lungs to various tissues and organs throughout the body. Similarly, in myoglobin, haem assists in oxygen storage and release within muscle cells.
Haem also serves as a prosthetic group in several important enzymes, such as cytochromes, catalases, and peroxidases. These enzymes utilize haem to carry out various chemical reactions, including electron transfer processes and breaking down harmful reactive oxygen species.
Additionally, haem can be found in some non-biological sources, such as heme-containing food products like red meat. It is also used in laboratory research and medical applications.
Overall, haem is a vital component for oxygen transport and enzymatic reactions, playing a crucial role in the proper functioning of several physiological processes in living organisms.
The word "haem" is derived from the Greek word "haima" (αἷμα) which means "blood". The Greek word "haima" ultimately comes from the Proto-Indo-European root "*h₁ésh₂r̥" which also meant "blood". This root is believed to be derived from the onomatopoeic sound of flowing blood. The word "haem" is commonly used as a prefix in medical and biological terms that relate to blood or blood components.
