Influence of inactivation of trypsin on immunoreactivity and serum immunoreactive trypsin concentration measured by radioimmunoassay.

The influences of various active site-specific reagents of trypsin and protease inhibitors on the immunoreactivity of trypsin and serum trypsin concentration have been studied by radioimmunoassay (RIA). The RIA using inactivated 125I-trypsin as tracer showed lower Bo/T than the RIA using active 125I-trypsin, but the coefficient of variance of the former was smaller than that of the latter. Normal serum trypsin concentrations were 26.12-36.38 ng/ml with the RIA using inactivated 125I-trypsin as antigen tracer, and 201.15 ng/ml with the RIA using active 125I-trypsin as tracer. The recovery experiment showed that the difference was due to the interaction of serum protease inhibitors and labeled active trypsin.