[Molecular and complex-chemical studies on methemoglobin from Chironomus thummi thummi and various isolated...

1. Six different hemoglobin (Hb) fractions were isolated and characterized from the larvae of Chironomus thummi thummi using column chromatographic procedures. 2. Chromatographic and sedimentation-analytic studies (sedimentation coefficients of 2.0 +/- 0.2 (S)) have shown three Hb fractions to exist basically in a monomeric form. The molecular weight of component M-2 was determined by sedimentation equilibrium technique to be 15,470 +/- 400. The dimeric Hb was found to have sedimentation coefficients of 3.0 +/- 0.1 (S) in the weakly acidic pH region. In alkaline milieu, the reversible dissociation proceeds into the monomeric molecules (S20, W = 1.9 +/- 0.1 (S)). Molecular weights vary between pH 5.7 and 9.8 not only with hydrogen ion concentration, but also with protein concentration in correspondence with a dissociation-association equilibrium consisting of monomers and dimers. 3. For the Hb fraction M-2, a friction ratio of f/fo = 1.03 was calculated, suggesting an almost spherical shape of this protein. In contrast, the dimeric component appears to have a much more asymmetric structure (f/fo = 1.19). 4. The indivdual MetHb fractions bind the ligands: fluoride, imidazole and azide with different affinities.