Binding properties of a highly potent and selective iodinated aminopeptidase N inhibitor appropriate for radioautography

Aminopeptidase N (APN) is a zinc metallopeptidase involved in the inactivat ion of biologically active peptides, The knowledge of its precise distribut ion is crucial to investigate its physiological role. This requires the use of appropriate probes such as the recently developed highly potent and sel ective radiolabeled APN inhibitor 2(S)-benzyl-3-[hydroxy(1'(R)-aminoethyl)p hosphinyl]propanoyl-L-3-[I-125]iodotryosine ([I-125]RB 129), Its binding pr operties were investigated using rat brain homogenates (K-d = 3.4 nM) or AP N expressed in COS-7 cells (K-d = 0.9 nM). The specific binding was 95% at [K-d], and preliminary autoradiography in intestine is promising. The decre ased affinity of [I-125]RB 129 (= 10(-6) M) for the (ED)-D-350 APN mutant, supports the critical role of E-350 in the amino-exopeptidase action of APN , (C) 2000 Federation of European Biochemical Societies.