An Analysis of the Proopiomelanocortin Systems in the Pituitary of the Squamate Reptile Lacerta galloti

Abstract

Acid extracts of the pars intermedia of the squamate reptile Lacerta galloti were screened for immunoreactive forms of proopiomelanocortin (POMC)-related end products following Sephadex G-50 column chromatography, α-MSH-sized end products were detected with a Val-NH 2, C-terminal-specific RIA, and β-endorphin-sized end products were detected with a separate C-terminal-directed RIA. Five peaks of α-MSH-related immunoreactivity were isolated following fractionation by reversed-phase HPLC. Based on a comparison of the reversed-phase HPLC properties and the net positive charges (pH 2.75) of the Lacerta forms of α-MSH to those of the mammalian forms of α-MSH and Anolis carolinensis ACTH(I-13)NH 2, it appears that the N-acetylation of α-MSH is a major post-translational processing event in the pars intermedia of L. galloti. Although multiple forms of β-endorphin were detected in the pars intermedia of L. galloti following cation-exchange chromatography, the low levels of N-acetylated β-endorphin detected with an N -acetyl-specific β-endorphin RIA indicate that the N-acetylation of β-endorphin in this species is a minor post-translational processing event. This pattern of POMC processing in the pars intermedia of L. galloti is similar to the processing events observed for the turtle Pseudemys scripta , but distinct from the processing events observed in the squamate reptile A. Carolinensis.