title: Calculation of the circular dichroism of Chironomus hemoglobin in the light of the quality of its X-ray structure.
abstract: For the larval hemoglobin III of the insect Chironomus thummi thummi, the rotational strength of the B (Soret) and Q band is calculated with a monopole/monopole and a dipole/dipole approximation applied to the atomic co-ordinates of the X-ray structures at 2.5 and 1.4 A resolution. In previous calculations using the 2.5 A co-ordinates and with perturbing groups being restricted to aromatic side-chains, the dipole/dipole approximation clearly confirmed the negative sign observed by experiment. The predominant interactions were those of phenylalanine residues. Recalculation with X-ray data refined to the present limits of performance corroborates the negativity of the rotational strength, but now the most important contributions are due to the peptide bonds formerly neglected. Also for the 2.5 A coordinates it is learned that in contrast to earlier expectation the influence of the backbone in this hemoglobin is rather strong. A substantial contribution is further obtained for the perturbation by one of the propionic acid carboxylate groups of the heme. Perspectives and problems of the approach are outlined.
mesh_terms: D000596:Amino Acids; D000818:Animals; D002942:Circular Dichroism; D004175:Diptera; D006454:Hemoglobins; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D000596:Amino Acids; D006454:Hemoglobins