title: Arsenazo III forms 2:1 complexes with Ca and 1:1 complexes with Mg under physiological conditions. Estimates of the apparent dissociation constants.
abstract: Experiments to determine the apparent dissociation constants of the Ca and Mg complexes of arsenazo III clearly indicated that the predominant Ca complex contains one Ca ion and two dye molecules, although previous reports have either claimed or assumed 1:1 complexing. The evidence is based on the effects of varying [dye] as well as [Ca] and [Mg], and clear evidence for the formation of 1:1 complexes with Ca was obtained only at submicromolar [dye], whereas Mg formed 1:1 complexes exclusively. The implications of these findings with regard to the use of arsenazo III as an indicator of intracellular free [Ca] are discussed, with particular reference to its selectivity for Ca and the interference effects of other ions.
mesh_terms: D001150:Arsenazo III; D001391:Azo Compounds; D002118:Calcium; D007700:Kinetics; D008274:Magnesium; D008433:Mathematics; D008954:Models, Biological
chemical_list: D001391:Azo Compounds; D001150:Arsenazo III; D008274:Magnesium; D002118:Calcium
references.citation: J Physiol. 1978 Feb;275:357-76
references.pmid: 633127
references.citation: J Physiol. 1977 May;267(2):299-320
references.pmid: 17732
references.citation: Proc R Soc Lond B Biol Sci. 1977 Aug 22;198(1131):201-10
references.pmid: 20641
references.citation: Anal Biochem. 1977 Dec;83(2):433-50
references.pmid: 603036
references.citation: Science. 1977 Apr 29;196(4289):531-3
references.pmid: 850795
references.citation: Biochim Biophys Acta. 1976 Nov 18;451(1):321-5
references.pmid: 827309
references.citation: Anal Biochem. 1976 Dec;76(2):487-501
references.pmid: 998987
references.citation: J Gen Physiol. 1976 Apr;67(4):433-67
references.pmid: 818340
references.citation: Biophys J. 1975 Nov;15(11):1155-60
references.pmid: 1201331