CALORIMETRIC ANALYSIS OF LISINOPRIL BINDING TO ANGIOTENSIN-I-CONVERTING-ENZYME

Isothermal titration microcalorimetry has been used to measure changes in enthalpy and heat capacity for binding of lisinopril to the angiot ensin I-converting enzyme (ACE; EC 3.4.15.1) and to its apoenzyme at p H 7.5 over a temperature range of 15-30 degrees C. Calorimetric measur ements indicate that lisinopril binds to two sites in the monomer of b oth hole-and apo-ACE. Binding of lisinopril to both systems is enthalp ically unfavorable and, thus, is dominated by a large positive entropy change, The enthalpy change of binding is strongly temperature-depend ent for both hole-and ape-ACE, arising from a large heat capacity chan ge of binding equal to -2.4 +/- 0.2 kJ/K/(mol of monomeric hole-ACE) a nd to -1.9 +/- 0.2 kJ/K/(mol of monomeric ape-ACE), respectively, The negative values of Delta C-p for both systems are consistent with buri al of a large non-polar surface area upon binding. Although the bindin g of lisinopril to hole-and ape-ACE is favored by entropy changes, thi s is more positive for the holoenzyme, Thus, the interaction between Z n2+ and lisinopril results in a higher affinity of the holoenzyme for this drug due to a more favorable entropic contribution. (C) 1998 Fede ration of European Biochemical Societies.