Heme vs Hemin

1. What is heme?
A red inorganic molecule.
Is found in rbc.
Is found in hemoglobin (Hb) and myoglobin (Mb); there are 4 hemes in Hb, and 1 heme in Mb.
Carries oxygen by binding; 1 heme binds 1 oxygen molecule.
Makes rbc red.
Makes blood appear bright red.

2. What is hemin?
A black inorganic molecule formed by heme oxidation (exposure to air).
Is found when rbcs burst open (lysed, destroyed) and exposed to oxygen in the air.
Formed from heme upon long standing outside the body.
Is formed in vitro.
Makes blood appear dark.

3. Are heme and hemin the same?
No.
Heme is functional when present inside intact rbcs.
Hemin is non functional; it is a dysfunctional molecule.

Fresh blood is bright red due to presence of heme in intact rbcs.

Stale blood is dark or black due to presence of hemin. Heme converts to hemin. The longer exposure to air, and greater conversion to hemin, the darker the blood.

External links:
http://en.wikipedia.org/wiki/Hemoglobin
http://en.wikipedia.org/wiki/Myoglobin