The role of pyridoxal and manganous ions in the synthesis of iodothyronines

Abstract

1. 1. The synthesis of 3,3′ diiodothyronine (3,3′T 2) from monoiodotyrosine (MIT) in an assay system containing MIT, pyridoxal, Mn 2+, thyroid microsomes, and a H 2O 2-generating system was studied. The yield of 3,3′T 2 was approx. 17% and was only slightly less if the microsomes were preboiled for 20 min. 2. 2. Omission of microsomes from the assay system and chromatography of a butanol extract of the system in butanol-acetic acid-water disclosed a component with R F 0.8 in 15% yield. The formation of this component depended on the presence of Mn 2+, MIT, and pyridoxal. Spectral analysis and other data indicated that it is a metal chelate of Mn 2+ with a Schiff base formed from pyridoxal and MIT. This metal chelate exhibits peroxidase activity which may be primarily responsible for the synthesis of 3,3′T 2 from MIT in the system studied.