Calmodulin is labeled at lysine 148 by a chemically reactive phenothiazine.
10-(3-Propionyloxysuccinimide)-2-(trifluoromethyl)phenothiazine (POS-TP) is a chemically reactive calmodulin antagonist: 2 mol are incorporated per mol of calmodulin when excess reagent is used, and only lysyl side chains are modified. Tryptic peptide mapping demonstrated that a single unique site on calmodulin reacts at low molar ratios of POS-TP. Labeled peptides were isolated and analyzed by amino acid composition and sequence analysis. The unique site was identified as Lys148 of calmodulin, the carboxyl-terminal residue. At higher molar ratios of the reagent Lys21, Lys75, and Lys77 are labeled as are several minor peptides that were not characterized.
D000345:Affinity Labels / Q000378:metabolism*; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002417:Cattle; D008239:Lysine / Q000378:metabolism*; D010446:Peptide Fragments / Q000032:analysis; D010640:Phenothiazines / Q000378:metabolism*; D013388:Succinimides / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism
D000345:Affinity Labels; D000596:Amino Acids; D002147:Calmodulin; D010446:Peptide Fragments; D010640:Phenothiazines; D013388:Succinimides; C042522:10-(3-propionyloxysuccinimide)-2-(trifluoromethyl)phenothiazine; D014357:Trypsin; D008239:Lysine