Detection of methylated asparagine and glutamine residues in polypeptides.
A residue of gamma-N-methylasparagine (gamma-NMA) is found at position beta-72 of many phycobiliproteins. delta-N-Methylglutamine is present in some bacterial ribosomal proteins. gamma-NMA was synthesized by reacting the omega-methyl ester of aspartate with methylamine and delta-N-methylglutamine by reaction of pyroglutamate with methylamine. These derivatives and the omega-methyl esters of aspartate and glutamate were characterized by melting point, by thin-layer chromatography, by amino acid analysis, by NMR spectroscopy, and after conversion to the phenylthiohydantoin (PTH) derivative. The gamma-NMA residues in peptides from allophycocyanin, C-phycocyanin, and B-phycoerythrin were stable under the conditions of automated sequential gas-liquid phase Edman degradation. On HPLC, PTH-gamma-NMA co-eluted with PTH-serine and was accompanied by a minor component eluting just prior to dimethylphenylthiourea. Similar results were obtained on manual derivatization of synthetic gamma-NMA to prepare the PTH derivative. The PTH-delta-N-methylglutamine standard eluted near the position of dimethylphenylthiourea under the usual conditions employed for the identification of PTH-amino acid derivatives in automated protein sequencing.
Klotz
A V
AV
Department of Biochemistry, Louisiana State University, Baton Rouge 70803.
Thomas
B A
BA
Glazer
A N
AN
Blacher
R W
RW
D000595:Amino Acid Sequence; D001216:Asparagine / Q000032:analysis*; D001419:Bacteria / Q000032:analysis; D002851:Chromatography, High Pressure Liquid; D005973:Glutamine / Q000032:analysis*; D006868:Hydrolysis; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008745:Methylation; D008969:Molecular Sequence Data; D010669:Phenylthiohydantoin / Q000378:metabolism
D005973:Glutamine; D010669:Phenylthiohydantoin; D001216:Asparagine