Xuegong Zhu - Academia.edu (original) (raw)

Papers by Xuegong Zhu

Journal of Chromatography B: Biomedical Sciences and Applications, 1993

Significant post-mortem changes in peptide concentration occur within the previously unstudied ti... more Significant post-mortem changes in peptide concentration occur within the previously unstudied timeframe, i.e. within 1 h, for the proenkephalin A, proopiomelanoccortin, and tachykinin neuropeptidergic systems in the pituitary. These data differ from data obtained in other studies that concluded that peptides are stable for up to 72 h post-mortem. The post-mortem stability of the three neuropeptides, methionine enkephalin, substance P, and beta-endorphin, was studied in the rat pituitary to test the hypothesis that significant post-mortem concentration changes of those three neuropeptides occur in the immediate post-mortem time period.

Peptides, 1997

containing proteins in the human pituitary. Peptides 18(9) 1399-1409, 1997-Two new proopiomelanoc... more containing proteins in the human pituitary. Peptides 18(9) 1399-1409, 1997-Two new proopiomelanocortin (POMC)-derived ␤-endorphin (BE)-containing proteins were detected in the human pituitary, using HPLC, trypsin digestion, and a high sensitivity search with liquid secondary ion mass spectrometry (LSIMS) for the protonated molecule ion, (MϩH) ϩ , of tryptic peptides that are unique to BE. Proteins were extracted from pituitary tissues and were purified by solid phase extraction (SPE) chromatography and RP-HPLC. Each HPLC fraction was treated with trypsin, and each unseparated peptide mixture was analyzed by LSIMS to detect the two selected marker peptides (BE 20-24 and BE 10-19) that have excellent LSIMS desorption-ionization properties. The detection of both of those peptides indicated the presence of BE-containing proteins in two HPLC fractions (number 47 and 51). Tandem MS determined the amino acid sequence of the marker peptide BE 20-24 (NAIIK), and those sequence data optimized the specificity of the method. The two new BE-containing proteins derive from the C-terminal region of POMC, and were minor components in the two HPLC fractions. The major component in fraction 51 derived from the vasopressin-neurophysin 2-copeptin precursor.

Mass Spectrometry Reviews, 1996

Biological Mass Spectrometry, 1993

In a study to test the hypothesis that defects in the metabolism of neuropeptides might be a cont... more In a study to test the hypothesis that defects in the metabolism of neuropeptides might be a contributing factor to human anterior pituitary tumor formation, the proenkephalin A, proopiomelanocortin (POMC), and tachykinin systems, which produce methionine enkephalin (ME), beta-endorphin (BE), and substance P (SP), respectively, were measured in patients who had a wide variety of pituitary tumors. Mass spectrometry was used to optimize the level of molecular specificity of the ME and BE analytical measurements, and radioimmunoassay was used to measure SP-like immunoreactivity (SP-li). Compared to data obtained from pituitaries from post-mortem controls, the non-secreting tumors contained a significantly lower amount of the POMC neuropeptide, BE. The lower ME level was not significant. However, two adrenocorticotrophic hormone (ACTH)-secreting tumors contained ME, BE, and SP-li amounts that were much higher than both the controls and nonsecreting tumors. These data suggest that a hypometabolism of the POMC precursor may be operating in non-secreting tumors, and that a hypermetabolism of the proenkephalin A, POMC, and tachykinin precursors may be operating in two ACTH-secreting tumors. These data demonstrate that mass spectrometry plays a critical role in the study of human pituitary tumors.

Journal of Chromatography A, 1998

This manuscript reviews the use of an off-line combination of liquid chromatography (LC) and mass... more This manuscript reviews the use of an off-line combination of liquid chromatography (LC) and mass spectrometry (MS) to quantify endogenous neuropeptides in biological tissues and fluids, and tandem MS (MS / MS) to optimize the molecular specificity of the quantification of native peptides. Reversed-phase high-performance liquid chromatography (RP-HPLC) was used to purify selected endogenous neuropeptides from biological tissues and fluids. Liquid secondary ion MS (LSI-MS), also known as fast atom bombardment (FAB), is used to desorb and to ionize the peptide. The corresponding stable isotope-incorporated synthetic peptide of each peptide is used as the internal standard (I.S.) for quantification. The measurement of methionine enkephalin (ME) and of b-endorphin (BE) in the human pituitary is described. This 1-31 analytical method offers the highest molecular specificity for the measurement of a fully post-translationally modified peptide.

Biochemistry, 2000

Mass spectrometric characterization of glycosylated interferon-y variants separated by gel electr... more Mass spectrometric characterization of glycosylated interferon-y variants separated by gel electrophoresis Glycosylated proteins in polyacrylamide gels were characterized by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and glycosidase digestion. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of natural, human interferon-y (IFN-y) showed two glycosylated variants with apparent molecular masses of 20 and 24 kDa. MALDI-MS of the intact IFN-y, electroeluted from the two bands, confirmed that these correspond to IFN-y molecules glycosylated at one or both of the two potential glycosylation sites, respectively. The peptide map obtained by MALDI-MS after digestion in the gel covers 92% of the IFN-y sequence and revealed an N-terminal pyroglutamate residue and one oxidized methionine residue. One glycosylated peptide was detected after treatment of the peptide mixture with neuraminidase, and the carbohydrate structure partially elucidated by sequential glycosidase digestion monitored by MALDI-MS. A second glycosylated peptide, due to a very heterogeneous glycan structure, could only be observed after separation of the peptides by high performance liquid chromatography (HPLC) .

Analytical Letters, 1994

Abstract The relationship between the use of peptidase inhibitors and the recovery of the three n... more Abstract The relationship between the use of peptidase inhibitors and the recovery of the three neuropeptides, s-endorphin (BE), methionine enkephalin (ME), and substance P (SP), from bovine pituitary was studied by using a combination of reversed-phase high performance liquid chromatography (RP-HPLC) purification and radioimmunoassay (RIA). Acetic acid (1 M) or Tris-HCl buffer (50 mM, pH 7.5) was used for tissue homogenization. The peptidase inhibitors bacitracin, bestatin, captopril, leupeptin, phosphoramidon, and thiorphan were added individually to the tissue before homogenization. RIA results showed that the maximum recovery of all three neuropeptides occurred with acetic acid combined with low temperature (4°C) for tissue extraction regardless of the presence of any of the inhibitors. At 37°C and in Tris buffer (pH 7.5), no inhibitor improved the recovery of any neuropeptide, except that bestatin improved the recovery of ME.

Peptides, 1995

Two opioid neuropeptides, methionine enkephalin (ME) and beta-endorphin (BE), and one tachykinin ... more Two opioid neuropeptides, methionine enkephalin (ME) and beta-endorphin (BE), and one tachykinin neuropeptide, substance P (SP), were quantified in 10 prolactin (PRL)-secreting human pituitary adenomas and in 10 control human pituitaries. Immunohistochemical techniques provided appropriate staining for PRL. Reversed-phase high performance liquid chromatography (RP-HPLC) was used to purify these three neuropeptides before their analysis, radioimmunoassay (RIA) was used for the quantification of SP-like immunoreactivity (SP-LI), and liquid secondary-ion mass spectrometry (LSIMS) was used for the qualitative and quantitative analysis of ME and a tryptic peptide of BE. This study shows that, for 90% of the cases studied here (excluding one hypothyroidism case), the tachykinin A neuropeptide SP-LI level is decreased, the POMC peptide BE level is not altered, and the proenkephalin A neuropeptide ME level is increased in these PRL-secreting tumors.