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Biomedical subjects

A W Phelan

Publications and source records attributed to A W Phelan.

7 recordsLinked to original sources
PubMed1996

Porcine fibrinogen glycopeptides: substrates for detecting endo-beta-N-acetylglucosaminidases F2 and F3(1).

Two different glycopeptides were isolated in high yield from a thermolytic digest of porcine fibrinogen. Edman analysis established their sequences as Val-Glu-Asn(CHO)-Lys and Val-Gly-Glu-Asn(CHO)-Arg. These sequences are nearly identical to the two human fibrinogen glycopeptides, Val-Glu-Asn(CHO)-Lys (gamma-chain), and Met-Gly-Glu-Asn(CHO)-Arg (beta-chain). The predominant carbohydrate moiety of both asialoglycopeptides was a biantennary oligosaccharide with a core alpha(1-->6)-linked fucose as reported earlier (Da Silva et al. (1994) Arch. Biochem. Biophys. 312, 151-157). Both glycopeptides can be dansylated and used as sensitive substrates for Flavobacterium meningosepticum endo-beta-N-acetylglucosaminidases F2 and F3. Porcine fibrinogen represents the best source for substrates with this oligosaccharide type that can be reliably produced in multimicromole quantities.

Acetylglucosaminidase↗
PubMed1993

2-Iminothiolane: a reagent for the introduction of sulphydryl groups into oligosaccharides derived from asparagine-linked glycans.

A facile method for introducing reactive sulphydryl groups into oligosaccharides was developed. 1-Amino-oligosaccharides generated from asparagine-linked glycans by peptide-N4(N-acetyl-beta-D-glucosaminyl) asparagine amidase (PNGase F) digestion were monitored by high-performance anion-exchange chromatography with pulsed amperometric detection and derivatized under optimal conditions with 2-iminothiolane-HCl. The resulting mercapto-butyramido oligosaccharides, which were obtained in high yield, were alkylated with a fluorescent reagent and used to selectively assay for endoglycosidases that hydrolyse di-N-acetylchitobiose linkages.

Asparagine↗
PubMed1987

Detection and quantification of peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidases.

A detailed study of the oligosaccharide specificity of the almond enzyme, peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase A, was undertaken by comparing the rate of release of intact oligosaccharide chains from defined glycopeptides of all significant classes. The oligosaccharide of a trisialo-triantennary pentaglycopeptide from fetuin was released at the highest rate. A procedure was developed for the isolation of this glycopeptide in high yield from 5 g fetuin. Sequence analysis established the structure as Leu-Ala-Asn(CHO)-Cys-Ser. The Cys(Cm) and the Cys(Ae) derivatives of the glycopeptide were reacted with 4-(dimethylamino)-azobenzene-4'-sulfonyl (dabsyl) chloride to yield a monosubstituted and a disubstituted glycopeptide respectively. This chromophore confers high sensitivity at 436 nm on a pentapeptide backbone having minimal bonds for protease cleavage. A procedure was developed wherein these dabsyl derivatives were used in a high-performance liquid chromatography assay. The dabsyl-pentapeptide was retarded significantly from the dabsyl-glycopeptide and provided a sensitive method (1-2 nmol) of detection of peptide-N4-(N-acetylglucosaminyl)asparagine amidase activity. Enzyme was detected in crude extracts of all eight seed sources surveyed. The enzyme from Pisum sativum was partially purified and its properties were compared with the corresponding enzyme from almonds.

Amidohydrolases↗
PubMed1984

Demonstration of peptide:N-glycosidase F activity in endo-beta-N-acetylglucosaminidase F preparations.

Endo-beta-N-acetylglucosaminidase F preparations from Flavobacterium meningosepticum have been found to contain peptide:N-glycosidase activity. Only the second activity, designated as peptide:N-glycosidase F, readily cleaves the beta-aspartylglycosylamine linkage of a fetuin triantennary complex glycopeptide, as shown by the isolation of the corresponding carbohydrate-free peptide containing aspartic acid and of an intact oligosaccharide with a di-N-acetylchitobiosyl moiety at the reducing end. Both activities in the mixture will hydrolyze a high mannose octaglycopeptide from ovalbumin, with the type of product formed being influenced by pH. At pH 4.0, only the endo-beta-N-acetylglucosaminidase F activity is functional, releasing octapeptide-GlcNAc and oligosaccharide-GlcNAc. At pH 9.3, the predominant cleavage is by peptide:N-glycosidase F at the glycosylamine bond, releasing octapeptide and oligosaccharide-GlcNAc-GlcNAc. This latter oligosaccharide is then hydrolyzed by endo-beta-N-acetylglucosaminidase F to oligosaccharide-GlcNAc plus GlcNAc.

Acetylglucosaminidase↗