Incorporation of bovine thyroid peroxidase in liposomes

In the microsomal fraction of thyroid glands, the temperature dependence of DPH fluorescence polarization showed a discontinuity in the range of 29-33 degrees C. The transition temperatures of DMPC, DPPC and DSPC are near to the observed for the microsomal fraction. So that, thyroid peroxidase (TPO) was incorporated into liposomes made with these phospholipids. When DPH was incorporated in this peroxidase-liposome complex, a less pronounced phase transition was observed in the profiles of temperature dependence of DPH polarization, and the incorporation of the enzyme decreased the Tc. Arrhenius plots of TPO incorporated into liposomes showed discontinuities at similar temperatures observed by fluorescence polarization. The decrease of transition temperature of liposomes induced by thyroid peroxidase incorporation suggests that this enzyme seems to need a fluid medium for its enzyme activity.