Bovine erythrocyte hemoglobin is used as a substrate for pepsin and other proteases.
Hemoglobin is composed of one globin plus four hemes; heme consists of protoporphyrin IX and ferrous iron. The iron content of human hemoglobin is 0.338% (w/w) which gives a minimal molecular weight of 16,520; however, ultracentrifugal and osmotic pressure measurements indicate an actual molecular weight four times the minimum molecular weight (Henry 1968).
