Binding of Lanthanides and of Divalent Metal Ions to Porcine Trypsin

Michael Epstein, Alexander Levitzki*, Jacques Reuben

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

77 Scopus citations

Abstract

The single binding site for Ca2+ on the porcine trypsin molecule was found to be capable of binding trivalent lanthanide ions as well as Y3+ and the divalent ions Mn2+ and Cd2+. The affinity of the lanthanide ions to trypsin depends strongly on their ionic radius; the smaller the lanthanide ion, the higher the binding constant. The affinity of metal ions to trypsin does not depend on their chemical similarity to Ca2+. The fluorescence of Tb3+ is enhanced 105-fold when bound to porcine trypsin. The pH dependence of the Tb3+ fluorescence indicates that the metal binding site of the enzyme consists of one or more carboxyl side chains. Measurements on the fluorescence excitation spectrum of the trypsin-Tb3+ complex reveal energy transfer from one or more tryptophans in close proximity to the bound metal ion.

Original languageEnglish
Pages (from-to)1777-1782
Number of pages6
JournalBiochemistry
Volume13
Issue number8
DOIs
StatePublished - 1 Apr 1974
Externally publishedYes

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