Determination of ZD9583, a thromboxane receptor antagonist, in human plasma and urine by liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry.

A liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry (LC-APCI-MS-MS) method is described for the determination of a thromboxane receptor antagonist (4Z)-6-((2S,4S,5R)-2-(1-(2-cyano-4-methylphenoxy)-1-methylethyl)-4 -(3-pyridyl)-3-dioxan-5-yl)hex-4-enoic acid (ZD9583, I) in human plasma and urine. Proteins in plasma and urine samples are precipitated using acidified acetonitrile. The resulting supernatant is chromatographed on a C8 reversed-phase chromatography column. Following the diversion of the solvent front from the mass spectrometer by a switching valve, the column eluate is passed on to the mass spectrometer via a heated nebulizer interface where the analyte is detected by multiple reaction monitoring (MRM). The method has a chromatographic run time of less than 2 min, a linear calibration curve with a range of 1-500 ng ml(-1) and intra- and inter-day precision estimates of less than 10% over the calibration range.

Purification and composition of a novel gastrointestinal tumor-associated glycoprotein expressing sialylated lacto-N-fucopentaose II (CA 19-9).

Monoclonal antibody 1116NS 19-9 (Mab 19-9) exhibits selective reactivity with human gastrointestinal carcinomas and recognizes a carbohydrate determinant (CA 19-9) defined as a sialylated lacto-N-fucopentaose II. A scheme was devised for the purification of a human gastrointestinal tumor-associated glycoprotein antigen expressing CA 19-9 from colorectal carcinoma cell line SW1116 culture media in high yield. The key steps in the purification were immunoaffinity column chromatography with Mab 19-9 followed by reduction and alkylation of the specifically bound proteins in the presence of 6 M guanidine hydrochloride and a second Mab 19-9 immunoaffinity fractionation. The purified CA 19-9 containing glycoprotein ran as a single band on sodium dodecyl sulfate-polyacrylamide gradient gels with an apparent molecular mass of 210 kilodaltons. In the absence of detergents, this purified glycoprotein apparently reassociated to form aggregates of 600-2000 kilodaltons molecular mass as determined by size-exclusion chromatography. Amino acid analysis of CA 19-9 containing glycoprotein revealed that serine, threonine, and proline together accounted for greater than 35% of the amino acid residues, consistent with a mucin-like structure for the protein. Carbohydrate compositional analysis, however, was in contrast to a typical mucin with a fucose:mannose:galactose:N-acetylgalactosamine: N-acetylglucosamine:N-acetylneuraminic acid molar ratio of 4:1:12:2.5:5:5. The presence of both N-acetylgalactosamine and mannose suggested that both O- and N-linked oligosaccharides may exist on CA 19-9 containing glycoprotein. Protein and carbohydrate analyses indicated that this novel tumor-associated glycoprotein was 85% carbohydrate by weight. This purification procedure may be applicable to the isolation of other epithelial tumor-associated antigens.

Structural characterization of oligosaccharides by high-performance liquid chromatography, fast-atom bombardment-mass spectrometry, and exoglycosidase digestion.

A method for structural characterization of oligosaccharides after preparing uv-absorbing derivatives is described. The derivatives can be rapidly analyzed and purified by high-performance liquid chromatography, with separation of various structures determined primarily by size and sugar composition. Derivatization requires as little as 0.5-1.0 nmol of oligosaccharide, and detection of down to 50 pmol of oligosaccharide is possible by monitoring absorbance at 229 nm. In addition, the carbohydrate portion of the derivative was found to retain its sensitivity to exoglycosidases, allowing sequential enzymatic digestions for determination of sugar sequence and anomerity to be performed. The derivatives also possessed a site of potential positive charge, making them amenable to analysis by fast-atom bombardment-mass spectrometry. Permethylation of the derivatives permitted their separation by capillary gas chromatography, thus allowing investigation of their structures by gas chromatography-mass spectrometry. The combination of these techniques will allow almost the complete structure of small amounts of oligosaccharides to be determined.

Biosynthesis of alpha-galactosidase A in cultured Chang liver cells.

An investigation of the structure and biosynthesis of alpha-galactosidase A (alpha-D-galactoside glycohydrolase, EC 3.2.1.22) and its N-linked oligosaccharide chains was undertaken by metabolic labeling of Chang liver cells with [2-3H]mannose, immunoprecipitation of the activity, and examination of the resulting immunoprecipitates. From cells pulse labeled for 3 h, two radioactive bands with Mr = 58,000 and 49,000 were detected by SDS-gel electrophoresis; following a 20-h chase, only the Mr = 49,000 band was observed. Examination of the oligosaccharide fraction derived from pulse-labeled enzyme revealed that 18% of the asparagine-linked oligosaccharides were complex and 82% were high-mannose type. After a 20-h chase, 48% of the oligosaccharides were complex and 52% were high mannose. The high-mannose oligosaccharides of alpha-galactosidase A immunoprecipitated from both pulsed and pulse-chased cells had the same mobilities as Man8-9GlcNAc on thin-layer chromatography and Bio-Gel P-4. Two fractions of complex glycopeptides derived from the alpha-galactosidase A of pulsed and pulse-chased cells had the same migration on Bio-Gel P-4 as glucose oligomers containing 14 and 19-39 glucose units. Based on their apparent size and their behavior on concanavalin A-Sepharose, the complex oligosaccharides are believed to be composed of tri- and/or tetraantennary structures.

Post-translational processing reactions involved in the biosynthesis of lysosomal alpha-N-acetylgalactosaminidase in cultured human fibroblasts.

The synthesis and processing of alpha-N-acetylgalactosaminidase and its oligosaccharides were studied by metabolic labeling of human skin fibroblasts with [2-3H]mannose or 32Pi, immunoprecipitation of the enzyme, gel electrophoresis of the immunoprecipitates, and examination of the radioactive oligosaccharides recovered from protein bands excised from the gels. The data suggest that the enzyme was first synthesized as a Mr = 65,000 precursor which was then processed to a mature Mr = 48,000 enzyme; only the Mr = 65,000 precursor was immunoprecipitated from the culture medium. The oligosaccharides were separated into two chromatographic species by Bio-Gel P-4 fractionation. The more retained species were determined to be high-mannose oligosaccharides containing 7 to 9 mannose residues. A portion of the more highly excluded oligosaccharides from the Mr = 65,000 band was hydrolyzed by alkaline phosphatase, and the resulting oligosaccharides migrated with the same mobility as Man8-9GlcNAc. This alkaline phosphatase-sensitive peak could also be labeled with 32Pi. These observations indicate that alpha-N-acetylgalactosaminidase was synthesized as a higher molecular weight precursor which contained phosphorylated high-mannose oligosaccharides.

A simple and sensitive cAMP phosphodiesterase assay using a modification of the Ba(OH)2-ZnSO4 precipitation method.

A modification of the zinc-barium precipitation method is described for the measurement of phosphodiesterase activity. This method differs from the previous precipitation method in that it measures the appearance of the 5'-AMP product in the precipitate rather than the disappearance of the cAMP substrate from the supernatant. The method is simple, rapid, accurate and possesses a high sensitivity. It can be used to measure both the calmodulin activatable and nonactivatable forms of the enzyme. The procedure can be applied to monitoring phosphodiesterase activity throughout the purification of the enzyme from various tissues.

Inability of parvalbumin to function as a calcium-dependent activator of cyclic nucleotide phosphodiesterase activity.

The calcium-sensitive phosphodiesterase-stimulating activity sometimes associated with parvalbumin preparations is due to contaminating (less than 0.1%) amounts of carp muscle CDR (calcium-dependent regulator)-like protein. This protein can be resolved from parvalbumins by Sephadex G-75 chromatography and has many characteristics of the CDR. Parvalbumin itself causes a nonspecific stimulation of phosphodiesterase at all calcium concentrations which, in the presence of CDR, can cause an apparent shift to a lower concentration of the calcium level required for half-maximal stimulation.