Conformational analysis of thyrotropin releasing factor.

Conformational energy calculations on thyrotropin releasing factor and on several of its analogues indicate that the central histidyl residue of the native molecule is in an extended conformation. Some derivatives (with a reduced biological activity) have an altered conformation. Since some substitutions leave the conformation unchanged but alter the biological activity, these substitutions must involve the sites responsible for binding of the hormone to its receptor.