title: Ntau- and Npi-histidinoalanine: naturally occurring cross-linking amino acids in calcium-binding phosphoproteins.
abstract: Two isomeric amino acid cross-links, Ntau-histidinoalanine and Npi-histidinoalanine have been isolated from calcium-binding phosphoprotein particles derived from the extrapallial fluid of the estuarine clam Rangia cuneata. The cross-links were identified and compared by 13C and 1H NMR spectroscopy and mass spectroscopy. In the phosphoprotein particles, 6% of the amino acid residues are involved in cross-linkages. This is the first demonstration of the occurrence of the isomer Npi-histidinoalanine.
mesh_terms: D000818:Animals; D049872:Bivalvia; D002135:Calcium-Binding Proteins / Q000302:isolation & purification* / Q000378:metabolism; D004151:Dipeptides / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D010750:Phosphoproteins / Q000302:isolation & purification* / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D002135:Calcium-Binding Proteins; D004151:Dipeptides; D010750:Phosphoproteins; C034124:histidinoalanine