Liquid chromatography studies on the enzymatic degradation of luteinizing hormone-releasing hormone analogues with off-line identification by mass spectrometry.

Several agonists of luteinizing hormone-releasing hormone (LHRH) are currently used for different therapeutic purposes, but relatively little is known about their metabolic fate after administration. This paper describes the application of high-performance liquid chromatography combined with off-line fast atom bombardment mass spectrometry to identify the degradation products resulting from the incubation of LHRH analogues with proteolytic enzymes. Three analogues, containing a psi(E,CH = CH) pseudo-peptide bond were synthesized and afforded to the assay to determine the resistance against alpha-chymotrypsin and subtilisin: [Tyr5 psi(E,CH = CH)Gly6]LHRH, [Gly6 psi(E,CH = CH)D,L-Leu7]LHRH and [Pro9 psi(E,CH = CH)Gly10 ]LHRH. The pattern of peptide metabolites identified by this method indicates that alpha-chymotrypsin degrades LHRH analogues at the Trp3-Ser4 and Tyr5-Gly6 bond, while subtilisin hydrolyzes only the Tyr5-Gly6 linkage. The results also indicate a possible stabilization of native amide bonds against enzymatic degradation by neighbouring psi(E, CH = CH) modifications.