Detection of serine proteinase inhibitors in human cornified cells

A screening test for serine proteinase inhibitors revealed trypsin and urokinase inhibitors in the extract of human cornified cells. No inhibition for α-chymotrypsin, thrombin or plasmin was detected. Characterization of the inhibitors separated with a Sephacryl S-200 gel column demonstrated that: 1) trypsin inhibitor with a molecular weight of 45,000 was labile to heat, acid and alkali and showed temporary inhibition, and 2) urokinase inhibitor with a molecular weight of 35,000 was found relatively stable and exhibited time dependent inhibition. Both were distinct from a known thiol proteinase inhibitor which showed high stability and immediate inhibition. Regulatory roles of serine proteinase inhibitors are postulated.