[Angiotensin-converting enzyme stability in the presence of zinc-ions different concentrations].

Stability of angiotensin-converting enzyme was studied as a dependence on the zinc-ions concentrations brining in the apo-enzyme. Our data were discussed in the terms of a set of initial permissible conformation conditions of a protein (conformation distribution). Apo-enzyme was shown to be able to the radiation activation that is disappearing in the presence of even 10(-6 )mol/l of the zinc-ions.

[Radioenzymatic investigation of membrane and soluble forms of angiotensin-converting enzyme in acetate-phosphate buffer]. / Radioénzimologicheskoe izuchenie membrannoi i rastvorimoi form angiotenzinprevrashchaiushchego fermenta v atsetatno-fosfatnom bufere.

The dose response of soluble and membrane forms of angiotensin-converting enzyme to gamma-irradiation is investigated at different pH values of the medium and at different concentrations of acetate-phosphate buffer. Membrane form of the enzyme is more stable shows principally other conformational equilibrium than the soluble form. "Splitted" activation peaks on the curves of the enzyme dose response are observed.

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.

[Radiation activation of angiotensin-converting enzyme during low-dose irradiation]. / Radiatsionnaia aktivatsiia angiotenzin-prevrashchaiushchego fermenta pri malykh dozakh oblucheniia.

Radiation activation of angiotensin-converting enzyme (respect to Cbz-Phe-His-Leu as substrate) was obtained at the gamma (137Cs, t(irr) = 10s-2h, D approximately 3 Gy)- and X (plasma foces source, t(irr) = 10(-9)s, Cu-filter, D approximately 2 x 10(-5) Gy)-irradiation. The inactivation of the horseradish peroxidase at the same X-irradiation dose (2 x 10(-5) Gy) took place. Based on the experimental data and on the mathematical model proposed by us we made a conclusion that the special points exist on the dose response curves. Besides, the deduction that an activation is a common process at radiation changes of the different enzymes follows from our model. The activation of tobacco peroxidase (in presence of Ca(2+)-cations and without them) and of recombinant horseradish peroxidase (in presence of H2O2) by gamma-irradiation was really observed (respect to guaiacol as substrate).