ABSTRACT
We find that a common mutation that increases angiotensin I-converting enzyme activity occurs with higher frequency in male patients suffering from refractory temporal lobe epilepsy. However, in their brains, the activity of the enzyme is downregulated. As an explanation, we surprisingly find that carbamazepine, commonly used to treat epilepsy, is an inhibitor of the enzyme, thus providing a direct link between epilepsy and the renin-angiotensin and kallikrein-kinin systems.
Subject(s)
Angiotensin-Converting Enzyme Inhibitors/pharmacology , Anticonvulsants/pharmacology , Carbamazepine/pharmacology , Epilepsy, Temporal Lobe/physiopathology , Peptidyl-Dipeptidase A/physiology , Alleles , Animals , Anterior Temporal Lobectomy , Disease Models, Animal , Dose-Response Relationship, Drug , Epilepsy, Temporal Lobe/genetics , Epilepsy, Temporal Lobe/pathology , Epilepsy, Temporal Lobe/surgery , Genotype , Humans , INDEL Mutation , Male , Mice , Mice, Inbred C57BL , Peptidyl-Dipeptidase A/genetics , Polymorphism, Genetic/genetics , Temporal Lobe/drug effects , Temporal Lobe/pathologyABSTRACT
An assay using fluorescence resonance energy transfer peptides was developed to assess angiotensin I-converting enzyme (ACE) activity directly on the membrane of transfected Chinese hamster ovary cells (CHO) stably expressing the full-length somatic form of the enzyme. The advantage of the new method is the possibility of using selective substrates for the two active sites of the enzyme, namely Abz-FRK(Dnp)P-OH for somatic ACE, Abz-SDK(Dnp)P-OH for the N domain, and Abz-LFK(Dnp)-OH for the C domain. Hydrolysis of a peptide bond between the donor/acceptor pair (Abz/Dnp) generates detectable fluorescence, allowing quantitative measurement of the enzymatic activity. The kinetic parameter K(m) for the hydrolysis of the three substrates by ACE in this system was also determined and the values are comparable to those obtained using the purified enzyme in solution. The specificity of the activity was demonstrated by the complete inhibition of the hydrolysis by the ACE inhibitor lisinopril. Therefore, the results presented in this work show for the first time that determination of ACE activity directly on the surface of intact CHO cells is feasible and that the method is reliable and sensitive. In conclusion, we describe a methodology that may represent a new tool for the assessment of ACE activity which will open the possibility to study protein interactions in cells in culture.
