Tyrosine residues ring orientation

The basic structure of T3 and T4 is that of thyronine, a substituted tyrosine [0-(4-hydroxyphenyl)tyrosine] (Figure 33-1). Iodine residues at positions 3 and 5 of the inner phenolic ring confer on the outer ring a preferred orientation approximately 120° to the plane of the inner ring (Figure 33-2). Hormonal activity is maximal when the following requirements are met ... 

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