3,5,3’5’-tetraiodothyronine

STEP 3 DEIODINATION

I

I

O

Tyr

Tyr

NH2

I

I

T4

“DEACTIVATION” PATHWAY

“ACTIVATION” PATHWAY

5-deiodination

5’- deiodination

SELENODEIODINASES

rT3

T3

I

I

I

I

O

Tyr

Tyr

O

Tyr

Tyr

CH2CHCOOH

NH2

NH2

I

I

3,5,3’-Triiodothyronine (T3)

3,3’,5’-Triiodothyronine (reverse T3)