摘要:
Earlier investigations have shown that the irreversible inhibition of delta -chymotrypsin with the axially substituted trans-3-(2,4-dinitrophenoxy)-2,4-dioxa-3 lambda (5)-phosphabicyclo[4.4.0]decan-3-one (=2-(2,4-dinitrophenoxy)hexahydro-4H-1,3,2-benzodioxaphosphorin 2-oxide) proceeds under inversion of the configuration at the P-atom, Since this assignment is based on the comparison of the respective chemical shifts with model compounds, the covalent nature of the binding interaction between enzyme and inhibitor was formulated in analogy. To prove this assumption, inhibition experiments were performed with the deutereted inhibitor (+/-)-trans-3-(2,4-dinitrophenoxy)-2,4-dioxa-3 lambda (5)-phospha(1,5,5-H-2(3))bicyclo[4.4.0]decan-3-one ((+/-)-6a). P-31{H-2}-NMR-Spectroscopic monitoring of the reaction of stoichiometric amounts of the enzyme with (+/-)-6a at pH 7.8 yielded the diastereoisomeric adducts 9 (-3.88 ppm) and 9' (-3.96 ppm). Comparing the P-31 chemical shifts of the corresponding deuterated covalent phosphoserine model compounds 8a/8a' (-6.70 ppm, axial) and 8b/8b' (-4.11/-4.13 ppm, equatorial) confirmed the inversion of the configuration at the P-atom. H-1-Correlated P-31{H-2}-NMR spectra revealed a cross peak of the Ser(195)-H-2 (4.35 ppm) with the P-atom of the inhibitor at -3.88/-3.96 ppm, thus establishing the covalent nature of the Ser(195)-O-P bond.