THE POSTTRANSLATIONAL MODIFICATION OF BETA-ENDORPHIN IN THE INTERMEDIATE PITUITARY OF THE TOAD, BUFO-MARINUS, INCLUDES PROCESSING AT A MONOBASIC CLEAVAGE SITE

Fractionation of an acid extract of 15 B. marinus intermediate pituita ries by a combination of gel filtration chromatography and cation exch ange chromatography revealed one major and five minor forms of beta-en dorphin in this tissue. Based on reversed-phase HPLC and immunological properties, as well as amino acid composition and primary sequence an alysis, it was deduced that the sequence of the major form of B. marin us beta-endorphin is N-acetyl-YGGFMTPE. Overall, the steady-state anal yses of the minor forms of beta-endorphin indicated that the posttrans lational processing of beta-endorphin in the toad intermediate pituita ry includes endoproteolytic cleavage at both paired basic and monobasi c cleavage sites.