Characterization of a sialate pyruvate-lyase in the cytosol of human erythrocytes.
Sialate pyruvate-lyases, also known as sialate aldolases (EC 4.1.3.3), reversibly catalyse the cleavage of free N-acetylneuraminic acids to form pyruvate and N-acetylmannosamine. These enzymes are widely distributed and are present in numerous pro- and eukaryotic cells, in which they are localized only in the cytosol. They play an important role in the regulation of sialic acid metabolism by controlling the intracellular concentration of sialic acids of biosynthetic or exogenous origin, thus preventing the accumulation of toxic levels of this sugar. Application of an original colorimetric micromethod for N-acetylmannosamine determination, as well as the use of [4,5,6,7,8,9-14C]N-acetylneuraminic acid, led us to evidence a cytosolic neuraminate aldolase activity in human red blood cells (RBCs) and then to define the main characteristics of this enzyme: Michaelis-Menten type, K(m:) 1.4 +/- 0.05 mM, optimal pH: 7.6 +/- 0.2, optimal temperature: 70 +/- 2 degrees C, inhibition by heavy metals: Ag(+) and Hg(++). These enzyme parameters are close to those of the bacterial and mammalian aldolases described up to now. At the moment, the presence of sialate pyruvate-lyase in the cytosol of red blood cells remains an enigma.
Bulai
Tatiana
T
Laboratorul de Biochimie, Facultatea de Biologie, Universitatea Alexandru Ioan Cuza, Bd-ul Copou no 11, 6600 Iasi-6, Romania.
Bratosin
Daniela
D
Artenie
Vlad
V
Montreuil
Jean
J
D001345:Autoradiography; D002250:Carbon Radioisotopes; D002384:Catalysis; D002412:Cations / Q000494:pharmacology; D002855:Chromatography, Thin Layer; D003600:Cytosol / Q000201:enzymology; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008670:Metals / Q000494:pharmacology; D019158:N-Acetylneuraminic Acid / Q000737:chemistry / Q000378:metabolism; D007652:Oxo-Acid-Lyases / Q000097:blood*; D019289:Pyruvic Acid / Q000494:pharmacology; D013379:Substrate Specificity; D013696:Temperature; D013997:Time Factors
D002250:Carbon Radioisotopes; D002412:Cations; D008670:Metals; D019289:Pyruvic Acid; D007652:Oxo-Acid-Lyases; C443820:sialate-pyruvate lyase; D019158:N-Acetylneuraminic Acid