Hemoglobins - Process of Respiration
Hemoglobins are the very well known of all respiratory pigments. The basic molecular unit of Hemoglobin contains a haem group bound to a protein or globin moiety. Haeme is a metalloporphyrin, to be much more specific, ferrous protoporphyrin. This serves as the prosthetic (serving as a prefix) group, with that is linked the protein. Hemoglobins of different species differ in their chemical and physical properties. These differences are attributable to differences in their globin moieties. The molecular weight of each unit molecule is usually about 16000 - 17000. The four-unit hemoglobin of vertebrates thus have molecular weights of almost 64090 - 68000. Relatively huge hemoglobin molecules are found in some non-chordates. For instance, in numerous annelids including earthworms (for example Lumbricus) and in the polychaete Arenicola the blood Hemoglobins has a molecular weight of nearly 3 million. Such large molecules frequently contain around 100 or more oxygen-binding sites.