Liquid chromatographic-mass spectrometric studies on the enzymatic degradation of beta-endorphin by endothelial cells.

An on-line HPLC-mass spectrometric procedure with an electrospray atmospheric pressure ionization (ESI-API) ion source was developed to identify the enzymatic degradation products (peptides) generated by incubation of human beta-endorphin (h beta E) with cultured aortic endothelial cells. The samples from the complex incubation mixture were prepurified and enriched using a small reversed-phase (RP) perfusion precolumn. Flow switching was applied to transfer the peptides from this precolumn to the analytical RP column of 2 or 0.

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.

Benzoylation of sugars, polyols and amino acids in biological fluids for high-performance liquid chromatographic analysis.

A precolumn benzoylation for analyzing sugars, polyols and neutral amino acids in biological fluids by high-performance liquid chromatography has been developed, which avoids protein precipitation, drying procedures and the use of pyridine. Derivatization and chromatography can be performed within one hour with a minimum detectable quantity of ca. 1 pmol (signal-to-noise ratio > 2).

Liquid chromatographic-mass spectrometric studies on the enzymatic degradation of gonadotropin-releasing hormone.

Gonadotropin-releasing hormone (GnRH) derivatives are used in cancer therapy, but relatively little is known about their metabolic fate in the organism. This paper describes the application of high-performance liquid chromatography combined with electrospray mass spectrometry to identify the degradation products resulting from the incubation of two GnRH analogues, D-Phe6-GnRH and DSer(OtBu)6-desGly10-GnRH-ethylamide (buserelin) with rat kidney membranes. Reversed-phase columns were applied with gradient elution using a flow-rate of ca.