Myoglobin iron coordination

Selected entries from Methods in Enzymology [vol, page(s)] Application in fluorescence, 240, 734, 736, 757 convolution, 240, 490-491 in NMR [discrete transform, 239, 319-322 inverse transform, 239, 208, 259 multinuclear multidimensional NMR, 239, 71-73 shift theorem, 239, 210 time-domain shape functions, 239, 208-209] FT infrared spectroscopy [iron-coordinated CO, in difference spectrum of photolyzed carbonmonoxymyo-globin, 232, 186-187 for fatty acyl ester determination in small cell samples, 233, 311-313 myoglobin conformational substrates, 232, 186-187]. 

Myoglobin, unlike cytochrome P450 , cytochrome c peroxidase, and horseradish peroxidase, normally functions as an oxygen transport protein rather than as an enzyme. However, the availability of an iron coordination site in the ferric and deoxy ferrous states makes possible a reaction between the hemoprotein and H2O2. This reaction produces a... 

In a living body, oxygen is transported or stored with the help of hemoglobin or myoglobin. Iron(II) ions have a coordination number of six. When a ferrous ion forms a chelate with a porphyrin, two of its coordination sites are still unfilled. Therefore, one of the functions of the polypeptide chain of hemoglobin and myoglobin is to provide a histidyl residue as a position where one of the nitrogen atoms links to the fifth coordination position of the iron ion, as shown in Fig. 9-2. 

Steady-state kinetics. Consider the interchange of 02 and CO coordinated to myoglobin, an iron porphyrin represented as PFe ... 

The iron of unoxygenated myoglobin lies 0.03 nm (0.3 A) outside the plane of the heme ring, toward His F8. The heme therefore puckers slightly. When O2 occupies the sixth coordination position, the iron moves to within 0.01 nm (0.1 A) of the plane of the heme ring. Oxygenation of myoglobin thus is accompanied by motion of the iron, of His F8, and of residues linked to His F8. 

Figure 6-1. Heme. The pyrrole rings and methylene bridge carbons are coplanar, and the iron atom (F62 ) resides in almost the same plane. The fifth and sixth coordination positions of Fej are directed perpendicular to—and directly above and below—the plane of the heme ring. Observe the nature of the substituent groups on the (3 carbons of the pyrrole rings, the central iron atom, and the location of the polar side of the heme ring (at about 7 o clock) that faces the surface of the myoglobin molecule.

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