Working with sheep preparations, the authors determined that the molecular structure of TRF (thyroid releasing hormone), is 2-pyrrolidone-5-carboxylyl-histidyl-L-proline amide. On page 324, they showed the molecular spatial configuration of TRF. They synthesized this substance in the lab and proved that “this substance has quantitative and qualitative physicochemical and
biological characteristics which are indistinguishable from those of the natural substance isolated from the sheep.”

Guillemin shared half of the 1977 Nobel Prize in Physiology or Medicine with Andrew Schally "for their discoveries concerning the peptide hormone production of the brain." The other half of the prize was awarded to  Rosalyn Sussman Yalow "for the development of radioimmunoassays of peptide hormones."

(Thanks to Juan Weiss for this reference and its interpretation.)