title: Instability of purified 9-kDa porcine intestinal calcium-binding protein in the absence of calcium.
abstract: Purified 9-kDa porcine intestinal calcium-binding protein (ICaBP, Calbindin D9K) is unstable when stored at 4 degrees C in the absence of Ca(II). Cleavage of the polypeptide occurs producing approximately 5.2- and 3.7-kDa fragments. The former dimerizes giving a species which migrates on sodium dodecylsulfate-urea gels with an Mr 13,700, in contrast to the observed Mr 11,000 for native ICaBP. The fragmentation also results in an irreversible loss of high affinity Ca(II) bound to ICaBP prevents fragmentation. The dimer can be isolated from aged preparations of apo-ICaBP and is stable on further storage with or without Ca(II) present. The observed molecular weights of the fragments along with the amino acid analysis and ultraviolet spectra of the dimer suggest cleavage of the polypeptide chain of ICaBP in the vicinity of residue 49.
authors.affiliation: Department of Chemistry, Bryn Mawr College, Pennsylvania 19010.
authors.forename: A
authors.initials: A
authors.lastname: Randolph
authors.forename: K G
authors.initials: KG
authors.lastname: Strothkamp
mesh_terms: D000596:Amino Acids / Q000302:isolation & purification; D000818:Animals; D017317:Annexin A6; D001665:Binding Sites; D002118:Calcium; D002135:Calcium-Binding Proteins / Q000302:isolation & purification*; D007413:Intestinal Mucosa / Q000378:metabolism*; D010446:Peptide Fragments / Q000302:isolation & purification; D013056:Spectrophotometry, Ultraviolet; D013552:Swine
chemical_list: D000596:Amino Acids; D017317:Annexin A6; D002135:Calcium-Binding Proteins; D010446:Peptide Fragments; D002118:Calcium