Hemoglobin apoprotein

Oxygenation of Hemoglobin Triggers Conformational Changes in the Apoprotein... 

For example, globin (apoprotein) + heme (a prosthetic group that contains iron in a porphyrin ring) = hemoglobin. In a slightly different usage, apoprotein in association" with lipid = lipoprotein vehicles that transfer cholesterol and triglycerides in the blood stream. 

According to ORD measurements of ferric HRP and its apoprotein, splitting of the heme appears to cause a reduction of the estimated a-helix content (260, 259). CD spectra of Japanese-radish peroxidase a have been interpreted as reduction of about 35% (upper limit) in the a-helix content upon removal of the heme with possible formation of / -structure. Differences between the oxidized and reduced forms of this peroxidase have been recorded (261) [see above, Myoglobin and Hemoglobin, ultraviolet region],... 

Both myoglobin and hemoglobin contain a prosthetic group (a nonpolypeptide part of a protein), namely heme. Prosthetic groups remain bound to the protein permanently, by covalent bonds, noncovalent bonds, or both. The protein without the prosthetic group is called an apoprotein. When an enzyme is involved, the apoprotein plus prosthetic group may be called the holoenzyme. 

The protein part of hemoglobin, the apoprotein, is folded into several a-helices that are packed together to form a compact molecule with a deep pocket in which heme is bound. 

The heme is then inserted into a protein to become a hemoprotein. In the case of non-covalently bound hemes (i.e. in hemoglobin and myoglobin, cytochromes h and P450, catalase, and peroxidases), the association between heme and apoprotein is spontaneous and does not require a catalyst. In contrast, the covalently bound hemes (e.g. cytochrome c) require... 

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