Partial Purification and Some Properties of Thyroid Peroxidase Solubilized by Extraction with n-Butanol

Thyroid peroxidase has been extracted In 100% yield from suspensions of frozen pig thyroid “microsomes” by treatment with aqueous n-hutanol at pH 8.9. The solubilized enzyme does not sediment at 105, 000 × g in 1 hour, is retarded on a Sephadex G-200 gel and contains no membrane-like structures detectable by electron microscopy. Additional purification of the aqueous butanol extract is achieved by isoelectric precipitation and ion-exchange chromatography on DEAE cellulose. The partially purified TPO is recovered in 90% yield, with a 55 fold increase in specific TPO activity over the homogenate and a final nucleic acid content of about 4%. The phospholipid content is reduced to 10–15% of the 105.000 × g particles.

The partially purified preparations catalyze the peroxidation of guaiacol and the iodination of moniodotyrosine. The preparation solubilized by butanol is subject to aggregation as either protein or ionic concentration is increased. Aggregation is partialis reversed by dilution of protein, reduction of ionic strength or by the addition of detergents.