The effect of thyroxine on transparency and PAPS synthesis in the avian cornea

The normal onset of developing corneal transparency, which begins on Day 14 of chick embryogenesis, can be accelerated by the in vivo application of exogenous thyroxine, as originally demonstrated by Coulombre and Coulombre (1964, Exp. Eye Res.3, 105–114). When thyroxine (5 μg) is injected at Day 6, measurements of ³⁵SO^2?₄ incorporation by corneal homogenates indicate that synthesis of 3′-adenosine phosphosulfate (APS) in the cornea is increased at Day 8, but not that of 3′-phosphoadenosine-5′-phosphosulfate (PAPS). Injection of hormone at Day 9 results in a precocious increase in corneal transparency at Day 12 and a corresponding increase in the synthesis of APS and PAPS.     

The effect of thyroxine and related compounds on the aerobic myeloperoxidase--catalysed oxidation of NADH

Thyroxine concentrations as low as 1 microM significantly stimulate compound III formation during aerobic oxidation of NADH by highly purified myeloperoxidase. This increased compound III formation is paralleled by an increased oxidation of NADH. Stimulation of various thyronine and tyrosine analogues was in the order T4 greater than T3 greater than 3,5-T2 (or triiodothyropropionic acid). Thyronine and diiodotyrosine had no significant effect. From the potencies of the various thyronines to stimulate compound III formation, the following structural features seem necessary: (1) Substitution of thyronine with four iodine atoms. (2) An amino group on the alanine side chain. (3) Both aromatic rings of thyronine.