A hydrophobic site on the surface of the angiotensin-converting enzyme molecule.

Using the hydrophobic fluorescent dye 8-anilino-1-naphthalenesulfonic acid (8-ANS), a hydrophobic site on the surface of the protein globule of angiotensin-converting enzyme (ACE) from bovine lung was found. The dissociation constant of the ACE-8-ANS complex was estimated as 1.5 +/- 0.2 microM. This hydrophobic site is far from the ACE catalytic sites because the binding of the hydrophobic dye does not influence ACE activity. Shielding of the ACE hydrophobic site due to the complex formation with 8-ANS or Triton X-100 resulted in pronounced stabilization of the enzyme against the action of water radiolysis products during gamma-irradiation of dilute solutions of ACE.