Summary
The technique of crossed immunoelectrophoresis has been used to study the binding
to purified antithrombin III (At III) of heparin and other mucopolysaccharides. The
technique was unable to detect differences among samples of whole heparin from various
manufacturers, but proved useful in studying the binding of heparin fractions; at
the same molarities, low and high molecular weight heparin fractions displayed equal
binding ability to At III. A semi-synthetic heparin analogue showed no evidence of
binding to At III, but a sample of heparan sulphate did interact with At III at a
concentration 3 times that of heparin. Samples of purified At III from four different
manufacturers all displayed heterogeneity with respect to heparin binding. A proportion
of the total At III did not bind to heparin and, in one sample, this non-binding material
constituted about 40% of the total. An antiserum made against purified At III contained
antibodies with different cross-reactivities against heparin bound and non-heparin
bound At III.
