Properties of rat brain dipeptidyl aminopeptidases in the presence of detergents.

Rat brain dipeptidyl aminopeptidases I to IV were assayed in the soluble and membrane-bound fractions of rat brain, and the effects of the detergents Triton X-100 and sodium deoxycholate on their activities were studied. Dipeptidyl aminopeptidases I and II were significantly inhibited in the presence of sodium deoxycholate, but were not affected by the presence of Triton X-100. However, dipeptidyl aminopeptidase III was not influenced by either detergent, whereas the activity of dipeptidyl aminopeptidase IV was stimulated in the presence of Triton X-100, but remained unaffected by deoxycholate. These effects were partially or totally reversed after detergents were removed from the medium with adsorbent polymeric beads. Although detergents may have different effects on each DAP activity, the behavior of each enzyme activity in the presence of these substances was similar regardless of their subcellular location. These findings suggest that, as with other aminopeptidases, each of these proteins corresponds to the same molecular species in two different cell compartments.