May 27, 1980

New calcium indicators and buffers with high selectivity against magnesium and protons: design, synthesis, and properties of prototype structures

Biochemistry
R Y Tsien

Abstract

A new family of high-affinity buffers and optical indicators for Ca2+ is rationally designed and synthesized. The parent compound is 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), a relative of the well-known chelator EGTA [ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] in which methylene links between oxygen and nitrogen are replaced by benzene rings. BAPTA and its derivatives share the high (greater than 10(5)) selectivity for Ca2+ over Mg2+ of EGTA but are very much less affected by pH changes and are faster at taking up and releasing Ca2+. The affinity of the parent compound for Ca2+ (dissociation constant 1.1 x 10(-7) M in 0.1 M KCl) may be strengthened or weakened by electron-releasing or -withdrawing substituents on the aromatic rings. The Ca2+ and Mg2+ affinities may further be altered by replacing the ether oxygens by heterocyclic nitrogen atoms. The compounds described are fluorescent Ca2+ indicators absorbing in the ultraviolet region; the very large spectral shifts observed on binding Ca2+ fit the prediction that complexation should hinder the conjugation of the nitrogen lone-pair electrons with the aromatic rings. Derivatives with quinoline nuclei are notable for their hig...Continue Reading

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Mentioned in this Paper

Buffers
Calcium [EPC]
Conjugation
Tissue Membrane
Derivatives
Magnesium Measurement
Ethylene Glycol Measurement
Calcium
Structure-Activity Relationship
Protoplasm

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