Reversed-phase chromatographic behaviour of beta-endorphin: evidence of conformational change

Conformational changes in beta-endorphin as studied by electrospray ionization mass spectrometry

Because of a wide range of physiological functions, the structure of beta-endorphin (BE) is of great interest. In this study, conformational changes in BE induced by methanol are explored with electrospray ionization-mass spectrometry (ESI-MS). Differences in the charge-state distribution (CSD) and the extent of hydrogen/deuterium (H/D) exchange were used to monitor the conformational changes. The latter experiments were conducted via time-resolved ESI-MS in a continuous-flow apparatus. Both these techniques demonstrate that BE exists in a random coil open structure in aqueous media, but it acquires a more compact conformation with increased concentration of methanol. The H/D exchange experiments reveal that BE forms 61% alpha-helix in mixed solvents.

Separation of neuropeptide Y diastereomers by high-performance liquid chromatography and capillary zone electrophoresis

Separation of analogues of neuropeptide Y (NPY) in which a single D-amino acid replaced the corresponding naturally occurring residue was performed by chromatographic techniques to ensure the quality of the synthetic peptides to be used for structural and biological studies. Of the 35 compounds, 28 were easily separated (alpha = 1.02-2.76) from native NPY by standard reversed-phase high-performance chromatography (RP-HPLC) methods using a Vydac C18 column and a gradient buffer system developed in our laboratory comprised of triethylammonium phosphate (TEAP) at pH 2.25 and acetonitrile at 40 degrees C. The identical diastereomers could be separated on the same solid support and by using 0.1% trifluoroacetic acid (TFA) as the mobile phase modifier, however separation factors were smaller and retention times were longer. Three of the remaining seven unresolved analogues were separated (alpha = 1.02-1.96) by changing the solid-phase support to Vydac diphenyl derivatized silica and a buffer system consisting of 0.1% TFA and acetonitrile. Of the four remaining unresolved analogues, only two could be separated by capillary zone electrophoresis (CZE) in 0.1 M sodium phosphate at pH 2.5, but all four were finally resolved by changing the electrophoretic buffer to 0.1 M TEAP buffer at pH 2.5. Migration times of the diastereomers differed by 0.2-2.0 min from that of the natural NPY. In addition to confirming the uniqueness of each isomer, this investigation demonstrated the expansive utility and high efficiency of the TEAP buffer system for both RP-HPLC and CZE as well as the difference in selectivity produced by the TEAP and TFA buffers in RP-HPLC.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of beta-endorphin in human plasma by high-performance liquid chromatography with electrochemical detection: validation of a method employing the simultaneous purification and concentration of beta-endorphin

The simultaneous purification and concentration of synthetic human beta-endorphin from plasma is described, which when used together with an appropriate isocratic high-performance liquid chromatographic-electrochemical detection (HPLC-ED) system allows the determination of elevated physiological levels of beta-endorphin. Purification of plasma was gained by flash-freezing in liquid nitrogen, acidifying with 100 microliters of trifluoroacetic acid (10%, v/v) per ml of plasma, thawing at 4 degrees C and centrifuging to remove any precipitate. Solid-phase extraction with silica sorbent was utilised, which allowed further isolation of the analyte, a method of concentration and a procedure whereby beta-endorphin could be transferred to the HPLC mobile phase. Silica sorbent demonstrated greater selectivity than C18 for synthetic human beta-endorphin and, in addition, provided improved recovery of this analyte when utilising elution volumes of 500 microliters or less. Proteolytic degradation and heparin-induced high-affinity binding in plasma were shown not to effect the recovery of beta-endorphin if blood was rapidly chilled and plasma quickly obtained, frozen and acidified. Validation of this purification/concentration method using [125I]beta-endorphin demonstrated a recovery of 85.6% which was not jeopardised when concentrating the sample twenty-fold. This provided an increase in the sensitivity of detection, when used in conjunction with HPLC-ED, from 5 ng/ml to 250 pg/ml.