title: The binding of arsenazo III to cell components.
abstract: The Ca2+ indicator, arsenazo III, binds to subcellular fractions of rabbit skeletal muscle with sufficient affinity that in living muscle containing 1--2 mM arsenazo III, the estimated free arsenazo III concentration is only 50--200 microM; 80--90% of the bound arsenazo III is associated with soluble proteins. The binding of arsenazo III to soluble proteins decreases the optical response of the dye to Ca2+; this is due to a decrease in the affinity of the protein-bound dye for Ca2+. Approximately half of the bound arsenazo III is released from the particulate fraction and soluble proteins upon addition of 5 mM Ca2+, suggesting that the Ca-arsenazo complex has lower affinity for the protein binding sites than the free dye. The Ca2+ binding to the soluble protein fraction of rabbit skeletal muscle is attributable largely to its parvalbumin content.
mesh_terms: D000818:Animals; D001150:Arsenazo III / Q000378:metabolism*; D001391:Azo Compounds / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D009124:Muscle Proteins / Q000378:metabolism; D009132:Muscles / Q000378:metabolism*; D010320:Parvalbumins / Q000378:metabolism; D011817:Rabbits; D012995:Solubility; D013054:Spectrophotometry, Atomic; D013347:Subcellular Fractions / Q000378:metabolism*
chemical_list: D001391:Azo Compounds; D002135:Calcium-Binding Proteins; D009124:Muscle Proteins; D010320:Parvalbumins; D001150:Arsenazo III; D002118:Calcium