Enzymatic Synthesis of Prolactin-Releasing Factor (PRF) by Rat Hypothalamic Incubates and by Extracts of Rat Hypothalamic Tissue: Evidence for “PRF Synthetase” 1

Summary

Prolactin-releasing factor (PRF), activity of rat hypothalamic fragments was increased after incubation in Krebs–Ringer bicarbonate buffer, an effect observed even when puromycin in a concentration sufficient to block new protein synthesis was added. In the presence of a mixture of twenty naturally occurring amino acids, ATP and MG²⁺, a dialyzed ribosome-free extract of rat hypothalamic tissue showed an increased amount of PRF activity as compared with extracts incubated in the absence of cofactors and amino acids. These observations suggest that PRF is formed by a mechanism not involving new protein synthesis. Since PRF is formed by soluble hypothalamic extracts in the presence of ATP and amino acids, it is proposed that this hypothalamic hypophysiotropic hormone is a polypeptide and is biosynthesized by a “PRF Synthetase.”