Heat stability of protein S Heerlen and wild-type protein S.

The APC-cofactor activity of protein S Heerlen and wild-type protein S was analyzed by means of a FVIIIa-degradation assay (described in “Materials and methods”) after exposure of the protein S to 55°C for various amounts of time. The 100% value represents the activity of protein S before the heat exposure. Means ± SEM of 3 independent experiments performed in duplicate are shown.