Behaviour of horseradish peroxidase in AOT reversed micelles

The activity and stability of horseradish peroxidase (HRP) solubilised in A OT reversed micelles in isooctane and decalin was studied using guaiacol (2 -methoxyphenol) as the electron donor. The activity of the enzyme in both reversed micellar systems increases with the water content until reaching a maximum value that remains fairly const ant for water contents higher than 3.05% (v/v) in isooctane and 2.20% in de calin. The effect of pH on the activity profile was studied in the system A OT/isooctane. The enzyme is fully active at pH 7 and 8 for water contents h igher than 3.05% (v/v) but it was completely deactivated at pH 9. The effec t of surfactant concentration on HRP activity was also investigated. At low water contents a strong dependence was observed, whilst no further activit y increase was observed for water content values higher than 2.7% (v/v). The stability of HRP was found to be strongly dependent on the water conten t of the system with higher levels of stability obtained for higher values of water content. HRP stability is also affected by the presence of substra tes. Whilst the stability increases markedly when the enzyme is incubated w ith guaiacol, it does not appear to be so strongly affected by the presence of hydrogen peroxide, at the concentrations studied.