Structures of Polymer-Heme Complexes

Shibata et al.u have reported on the heme complexes of poly(L-histidine) and the copolymer of L-histidine and L-glutamic acid. Poly(L-histidine) and the copolymer formed the six-coordinate and five-coordinate heme complex, respectively. Hatano12 found that the formation constant of the complex of heme with poly(N-vinyl-2-methylimidazole) 3 was larger by a factor of 102 or 103 than that of the corresponding monomeric heme complex. 

In this section, the complex formations and the coordination structures of ferri- and ferro-protoporphyrineIX(ferriheme and ferrohem, respectively) 22 with 

The n values of the PLL-ferriheme and -ferroheme complexes in Table 4 are equal to 2, and the six-coordinate heme structure is formed preferentially this may be due to an inherent factor in which PLL differs from the other polymer ligands. 

It is well known that PLL can assume an a-helical conformation above pH 10. The complex formation between PLL and heme was carried out at pH 12, where the e-amino groups of the side chain of PLL were not protonated and PLL formed a complete a-helix14. The helix parameter (molar dlipticity at 222 nm) was the same before and after complex formation with heme. The helix content, Le. the overall conformation of PLL, was not affected. The viscosity of the PLL solution also remained constant on the addition of ferriheme14. These results mean that complex formation occurs with a structure complementary to the a-helical conformation and that bending of the PLL helix does not occur. The inter-polymer sandwich structure proposed by Blauer [Fig. 4(c)]9 is thus ruled out. The structure 

Ligand Solvent n Ferriheme Ferroheme K (1/molforn Ferriheme = 1 l2/mol2 forn = 2) Ferroheme 

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Fig. 4. Schematic representation of the structure of polymer-heme complexes the ferriheme complex with poly(4-vinylpyridine) (a), poly(L-lysine) (b), (c), or poly(7-benzyl-L-glutamate) with a pendant imidazole (d)...

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