Angiotensin I converting enzyme of rat intestinal and vascular surface membrane

High levels of angiotensin I converting enzyme are present in rat intestinal mucosa and in intestinal arteries. Homogenates of both tissues were subfractionated and fractions enriched in vascular plasma membrane or intestinal brush border were prepared. The preparations were identified and their purities established by marker enzyme enrichment and/or electron microscopy. Converting enzyme activity was highly enriched on both the vascular plasma membrane and the intestinal brush border. Subsequently the properties of these membrane-bound enzymes were compared. Both surface membrane-bound enzymes were highly sensitive to inhibition by captopril (SQ 14225) and teprotide (SQ 20881). Similar to converting enzyme isolated from other sources, they were also inhibited by bradykinin, angiotensin I, EDTA and o-phenanthroline. Finally, both membrane-bound enzymes were relatively resistant to activation by sonication, freezing and thawing or detergent. These results demonstrate significant similarities between surface membrane-bound converting enzyme from vascular and non-vascular sites. In addition, in view of the possible relationship of kinins and angiotensins to gastrointestinal function and blood flow, inhibition of gastrointestinal converting enzyme by captopril may affect some aspects of intestinal physiology.