Reconstitution of a purified and partially active low Km iodothyronine 5'-deiodinase with phospholipids

We previously reported the detergent-extraction and purification to homogeneity from rat liver microsomes of an iodothyronine 5'-deiodinase which differed from the type I enzyme in its molecular size as well as its Km, thiol responsiveness, and its expected sensitivity to the antithyroid drug, propylthiouracil. The specific activity enhancement (22-fold) of the delipidated enzyme was, however, relatively modest. We report here that the purified enzyme can be activated a further 25-fold by reconstitution in microsomal phospholipids and, to a lesser extent, in soybean phospholipids. The data suggest that a native lipid environment is necessary for proper conformation of the enzyme for optimal activity.