Pathways of degradation of buserelin by rat kidney membrane

The pathways of in vitro degradation of the gonadotropin-releasing hormone (GnRH) analog buserelin [pGlu-His-Trp-Ser-Tyr-D-Ser(tBu)-Leu-Arg- ProNHEt, B1-9] by the rat kidney membrane fraction was investigated using high-performance liquid chromatography for the separation of the peptide products and electrospray mass spectrometry for their identification. The N-terminal peptides B1-4, B1-3, B1-2, C-terminal peptides B3-9, B4-9, B5-9, B6-9, middle sequence B3-4 and the amino acids Trp, Ser and Tyr were found to be formed. However, due to extreme differences in the stability of the peptides toward the battery of membrane enzymes (B1-2, B6-9 >> B1-3, B5-9 >> B1-9 >> B1-4 > B4-9 > B3-9, B3-4), the final products of buserelin degradation were B1-2, B1-3, B5-9, and B6-9 and the amino acids Ser and, corresponding to the formation of B1-2 and B6-9, Trp and Tyr, respectively. The sequences B3-9, B4-9 and B3-4 were clearly detectable only when the inhibitors of aminopeptidases amastatin and bestatin were included in the incubations.(ABSTRACT TRUNCATED AT 250 WORDS)