Binding of long chain alkyl sulphates to equine ferric myoglobin.

The research explores the impact of long chain alkyl sulphates, including dodecyl sulphate, on equine ferric myoglobin. It contradicts prior hypotheses of an all-or-none type reaction, suggesting that binding occurs in several stages, resulting in different complexes, and that ferric myoglobin retains its native structure during this process, given a limit to the number of bound sulphate anions.

Study of Reaction Equilibrium

• The experiment was centered on the reaction of ferric myoglobin with alkyl sulphates, particularly dodecyl sulphate and those of different chain lengths.
• Investigation was carried out over varying protein concentration ranges.
• The spectral changes in ferric myoglobin, resulting in the transformation to a haemichrome or parahaematin, were carefully analyzed.
• Results were gauged through spectrophotometric measurements and equilibrium dialysis experiments.

Debunking Previous Hypotheses

• Previously, the majority opinion, based solely on spectral changes, propounded the all-or-none type reaction theory. This suggested that 18 detergent anions bind to one ferric myoglobin molecule.
• The results obtained demonstrated a discrepancy with former beliefs, providing evidence of a more complex reaction process.

New Conclusions on Alkyl Sulphates and Myoglobin Binding

• The first stage of association involves the binding of one dodecyl sulphate molecule to ferric myoglobin, without affecting the latter’s absorption characteristics.
• Further association takes place with another 3 or 4 molecules of dodecyl sulphate. This causes the conversion of ferric myoglobin to ferric myochrome, identifiable by its haemichrome absorption spectrum.
• Additional binding of dodecyl sulphate molecules to the myochrome happens in multiple discrete steps. This results in a wide array of complexes co-existing in the reaction medium.

Association Compounds Characterization

• The research suggests that these complexes maintain the ferric myoglobin’s original structure, provided that the number of bound dodecyl sulphate anions is at or below 50.
• The association compounds can be depicted as low-spin coordination complexes, with a second imidazole that originates from histidine E7 occupying the sixth coordination site of the iron atom.