Oxygen carriers, myoglobin

Pancreatic ribonuclease Staphylococcal nuclease Peroxidases Glutathione peroxidase Cytochrome c peroxidase Oxygen carriers Myoglobin, hemoglobin Myohemerythrin, hemerythrin Hormone-binding proteins Uteroglobin Pre albumin Lectins... 

Fe" porphyrins (hemes) are air sensitive and easily oxidized to the p-oxo dimer [Fe "(Por)]20 (Scheme 17). However, the irreversible oxidation can be prevented by a large excess of the axial ligand (retards process A), at a low temperature (< — 50 C, retards process D), or by protection of the O2 binding site (prevents process C). The third approach has been intensively studied in relation to the biological oxygen carriers, myoglobin (Mb) and hemoglobin (Hb). 

The two most important metalloprotein, other than hemoglobin and myoglobin are hemerythrins and hemocyanin which act as natural oxygen carrier. Hemocyanin is discussed in previous question. 

Myoglobin (Mb) consists of one heme group bound to a single polypeptide. It is present in heart and skeletal muscle. Mb functions both as a reservoir for oxygen, and as an oxygen carrier within the muscle cell. 

A number of model compounds have been synthesized which have Fe(ll)-porphyrin rings carrying a side chain with histidine arranged to be able to coordinate with the metal on one side. Several of these substances show promise as oxygen carriers with properties similar to myoglobin. 

These superoxo complexes are relevant models for the naturally occurring oxygen carriers hemoglobin and myoglobin, which contain ferroprotoporphyrin IX as an active center in which the sixth axial postion is occupied by the imidazole moiety of histidine.17 They also intervene as primary oxygen adducts in enzymatic cytochrome P-450 oxygenases.18... 

The absorption spectrum of cytochrome o (128) is also reported in Table 6. In many respects it too is like myoglobin but it reacts with oxygen rather than picking it up. Thus it is a terminal oxidase and not an oxygen carrier. 

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