Piyawan SurinrutJisnuson SvastiRudee SuraritMahidol University2018-10-122018-10-121981-05-14BBA - Enzymology. Vol.659, No.1 (1981), 38-47000527442-s2.0-0019879693https://repository.li.mahidol.ac.th/handle/123456789/30228Modifications have been made to the previous purification procedure so that electrophoretically homogeneous acidic protease (EC 3.4.23.-) proenzyme of specific activity 800 units/mg may be isolated from human seminal plasma with a yield of over 50%. The intrinsic fluorescence of the proenzyme shows maximum excitation and emission wavelengths at 280 and 340 nm, respectively, typical of proteins containing tryptophan. Complete activation causes a 30-35% decrease in intrinsic fluorescence, accompanied by a shift in λmaxto the blue of 4-6 nm. Time course studies indicate that acidification of proenzyme to pH 3.1 leads to a sudden large decrease in fluorescence that precedes both the appearance of active enzyme band on sodium dodecyl sulphate (SDS)-polyacrylamide gels and the generation of enzyme activity as detected by the turbidimetric milk clotting assay. These results suggest that acidification causes a rapid conformational change which promotes the release of the activation peptide from the proenzyme to yield the active enzyme. © 1981.Mahidol UniversityMedicineArticleSCOPUS10.1016/0005-2744(81)90269-2