ENZYMATIC METHYL ESTERIFICATION OF PITUITARY POLYPEPTIDES

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Abstract
Methyl esterification of pituitary polypeptides by protein methylase II (S-adenosylmethionine:protein-carboxyl O-methyltransferase, EC. 2.1.1.24) has been investigated. Ovine lutropin and adrenocorticotropin** (α1–39-ACTH) were found to be good methyl acceptor substrates, followed by β-lipotropin. While the α-subunit of lutropin had nearly equal the methyl accepting activity of lutropin, the β-subunit was devoid of accepting activity. The maximum amount of esterification occurred between 15 and 30 min (at 37° C) depending on the methyl acceptor molecule. The rate of the methyl esterification of adrenocorticotropin fragments was also studied. While α7–38-ACTH had less than half of α1–39-ACTH methyl accepting capacity, α1–17-ACTH did not serve as methyl acceptor. However, when a mixture of the two fragments was preincubated, the resulting mixture had full α1–39-ACTH activity.