Angiotensin-converting enzyme: presence of high activity in choroid plexus of mammalian brain.

The activity of angiotensin-converting enzyme in rat choroid plexus was higher than that of any other organ, being 6--7 times higher than that in lung and more than 50 times higher than in any other region of brain. Rabbit choroid plexus also had high activity of enzyme while that of human choroid plexus was relatively low. The enzyme in rat choroid plexus showed similar biochemical properties to that in other tissues; it was inhibited by the nonapeptide SQ 20,881, by (Sar1-Ala8)-angiotensin II and by EDTA, and required chloride ions for activity. As in other tissues, the choroid plexus enzyme was associated with particulate fractions after differential centrifugation. The corpus striatum and substantia nigra had the highest activities in the various brain regions examined.