Angiotensin IV displays only low affinity for native insulin-regulated aminopeptidase (IRAP)

Radioligand binding studies revealed that Ang IV binds to IRAP/'AT4 receptors' with high affinity. Yet, as these experiments were routinely done in the presence of chelators, only the catalytic zinc-depleted apo-form of IRAP was labelled. While the chelators remove the catalytic zinc from IRAP and protect Ang IV from proteolytic degradation, the Aminopeptidase N selective inhibitor '7B' only exerts the latter effect. By using 7B along with the new stable Ang IV-analog [3H]AL-11, we here show that the native enzyme is only a low affinity target for Ang IV.