Naturally-occurring pituitary growth hormone is phosphorylated.

The results of this communication show that ovine growth hormone (oGH) contains organically-bound phosphorous. The phosphorous content of growth hormone, lot S-11, is 1:3 (mol/mol) and that of lot S-12 is 1:6 (mol/mol). Results of 31P NMR studies suggest that the phosphorous exists in two chemical forms: as a monophosphoryl ester and as a phosphodiester. Evidence is provided which demonstrates that growth hormone can be phosphorylated in vitro with the catalytic subunit of protein kinase.