Sensitivity of chimeric proteins to blood-proteinases. (A) TSac and TS-SAPA proteins were incubated with normal mouse serum and assayed for trans-sialidase activity in samples taken at different times. Data are expressed as the mean ± SD. (B) GST or GST-SAPA protein incubated either with mouse serum or mouse blood for the indicated times, were assayed for proteolytic degradation as indicated in Materials and Methods. Controls are indicated as − (mouse serum alone) and + (GST or GST-SAPA–purified protein in PBS). (MK) Molecular weight markers (in kD) are indicated at right.