Characterization of Purified Heterologous Pituitary Luteinizing Hormones by Dinitrophenylation, Digestion with Carboxypeptidase A and Hydrazinolysis1

Abstract

Purified preparations of ovine, human, bovine and porcine pituitary luteinizing hormones (LH) have been characterized in terms of their response to dinitrophenylation, digestion with carboxypeptidase A and hydrazinolysis. Dinitrophenylation of ovine, bovine and porcine LH showed serine, threonine and phenylalanine to be the major amino acids detected. Serine was also found in human LH, along with high levels of valine and aspartic acid. Threonine and phenylalanine were relatively lacking in the human LH fractions studied. Carboxypeptidase A digestion released serine, and then leucine, from ovine and bovine luteinizing hormone. Serine and leucine, as well as glycine, were released rapidly from human and porcine LH, although the sequence of release was not as clear cut as with the ovine and bovine hormones. Hydrazinolysis revealed serine as a major residue in each species LH, together with suprisingly large amounts of phenylalanine. The results are interpreted as reflecting interesting patterns of similarity and instances of dissimilarity in the response of the LH fractions to the procedures employed, but are not necessarily considered to reflect the true nature of the C- and/or N-terminal amino acids of luteinizing hormone. The implications of the results in terms of assessment of homogeneity for currently available LH preparations of high specific activity are also discussed.