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 language | English |
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Pages (from-to) | 1777-1782 |
Number of pages | 6 |
Journal | Biochemistry |
Volume | 13 |
Issue number | 8 |
DOIs | |
State | Published - 1 Apr 1974 |
Externally published | Yes |