Synthèse
Volume 11, Numéro 1, Pages 1-8

Comparative Chemical Compositions, Physicochemical And Enzymatic Properties Between Pulmonary And Soluble Angiotensin I- Converting Enzymes

Authors : Baudln Bruno . Tahraoui Abdelkrim . Beneteau-burnat Benedicte . Robic Daniel . Giboudeau Jacqueline .

Abstract

Angiotensin I-converting enzyme (ACE) was purified from pig lung and serum to compare their physicochemical, catalytic and chemical properties with a particular focus on their sugar moieties; pig and rat pulmonary enzymes were also compared. For the three formsof ACE the molecular mass Was 172 ± 4 kDa on SDS-PAGE. The isoelectric point (pi) was 4.4 - 4.8 for both pulmonary ACEs but lower for serum ACE (4.3 - 4.6) ; neuraminidase increased both pi to 4.8 - 5.2. Serum and lung porcine ACEs exhibited identical Km, .Kcat, optimal pH and optimal chloride activating concentration for two synthetic specific substrates. From amino-acid analysis, slight differences were shown .between serum and pulmonary ACEs, and between pig and rat, in particular both pulmonary forms contained more . hydrophobic amino-acids. From sugar analysis, serum ACE was more glycosylated (11.9%) than pig and rat lung enzymes (8.6% and 8.8%, respectively); neither of the three ACEs contained N-acetylgalactosamine but only the sugars characteristic of N-glycosylation. Pig serum ACE was richer in N- acetylneuraminic acid than the pulmonary from that corroborates with differences in pI; both forms presented sugar molar ratios prediting mixtures of N- acetyllactosaminic and oligomannosidic chains, or hybrid structures, for rat lung ACE also but differently. Thus, membrane-bound and soluble ACEs have different chemical compositions that could correspond to translational and post-translational events in the endothelial cell, in particular for anchoring of the membrane-bound form and for excreting a soluble form protected against hepatic lectins. Nevertheless, the differences on amino-acid and sugar compositions have no influence on ACE catalytic properties.

Keywords

angiotensin I-converting enzyme; endothelium; isoelectric point; glycoproteins; membranous enzymes.

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