The increase in human antithrombin III tryptophan fluorescence produced by heparin

The increase in fluorescence of human antithrombin III has been used to study the binding of a semi-synthetic heparin analogue. One molecule of heparin were found to bind with an association constant of 8.9 . 10(4) M-1. The intrinsic fluorescence of antithrombin III exhibits a fluorescence quantum yield of 0.17. Upon addition of heparin a marked increase in the protein fluorescence quantum yield is observed.