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On the mechanism of enzyme action. LVII. Interaction between trypsin and ovomucoid

1954; Elsevier BV; Volume: 52; Issue: 2 Linguagem: Inglês

10.1016/0003-9861(54)90145-9

1096-0384

J. Sri Ram, L. Terminiello, M. Bier, F. F. Nord,

Enzyme Catalysis and Immobilization

Trypsin, ovomucoid, and their equimolecular complex have sedimentation constants of 2.5, 2.4, and 3.7 – 3.9 S, respectively. While trypsin can bind only one ovomucoid molecule, ultracentrifugal and electrophoretic data show that more than one molecule of trypsin can react with each molecule of ovomucoid. The dissociation constant of the equimolecular complex is 5.8 × 10−9M and of the complex involving two trypsin and one ovomucoid molecule is about 2.5 × 10−6M, as dedetermined by activity measurements. The isoelectric points of the two proteins and their equimolecular complex are at about pH's 10.8, 4.3, and 9, respectively. The complex behaves on electrophoretic examination as an independent protein, stable over an extended pH range, and dissociating only around pH 3.8. The trimolecular complex has a mobility intermediate between that of the equimolecular complex and free trypsin. It has a more limited pH range of stability, and dissociates readily around pH 6. The presence of either of the complexes does not cause a change in the electrophoretic mobilities of the other components present. The inhibition of trypsin by ovomucoid is considered to be another instance of competitive substrate inhibition.