Catalytic versatility of erythrocyte carbonic anhydrase. IX. Kinetic studies of the enzyme-catalyzed hydrolysis of 3-pyridyl and nitro-3-pyridyl acetates

Abstract

The present investigation demonstrates that bovine carbonic anhydrase powerfully catalyzes the hydrolysis of 3acetoxypyridine, 3-acetoxy-2-nitropyridine, and 3-acetoxy-2,6-dinitropyridine. The reactions follow Michaelis-Menten kinetics over the whole range of substrate concentrations studied, including the region [S] > Km. The pH-activity profiles are approximately sigmoid; the esterase activity is very small below pH 6 and rises to an intermediate plateau above pH 8. The inflection point at 25.0°lies at pH 7.56 for 3-acetoxy-2-nitropyridine and pH 7.4 for 3-acetoxy-2,6-dinitropyridine. A more detailed treatment of the data shows that for all these substrates the mild variation of Km with pH is dictated by the respective turnover number (ki) while the formal binding constants (ki/k-i) are nearly independent of pH

Plant carbonic anhydrase. Properties and bicarbonate dehydration kinetics

“…It certainly has not escaped our attention that the role of carbonic anhydrase may be to catalyze reactions other than the interconversion of CO2 and HCO3-. The catalytic versatility of erythrocyte carbonic anhydrase is well-established with respect to hydration of aldehydes (Pocker & Meany, 1965Pocker & Dickerson, 1969) and hydrolysis of esters (Tashian et al, 1964;Pocker & Stone, 1965Verpoorte et al, 1967;Pocker & Watamori, 1971;Pocker & Guilbert, 1972. For example, it has been demonstrated that the aldolase and the isomerase were specific for the keto rather than the hydrated form of glyceraldehyde 3-phosphate (Reynolds et al, 1971).…”

Water in enzyme reactions: biophysical aspects of hydration-dehydration processes

“…Enzyme-substrate and enzyme-inhibitor interactions are not random, but rather specific, usually involving the participation of specific residues from the enzyme interacting with specific regions of the substrate or inhibitor directly [99,100]. Many direct interactions with substrates and inhibitors require that the water be displaced first [42,[88][89][90][91][92][93][94][95][96][97][98]101]. Clearly, the nature of its interaction with the enzyme must be understood before any more detailed discussion is attempted.…”

In Situ Ligand Transformation for Two-Step Spin Crossover in FeII[MIV(CN)8]4– (M = Mo, Nb) Cyanido-Bridged Frameworks

“…By checking a number of pyridine derivatives, we found that two closely related ligands, 3-acetoxypyridine (3-OAcpy) and 3-hydroxypyridine (3-OHpy), could appear simultaneously in the aqueous solution of Fe II (3-OAcpy)− [M(CN) 8 ] n− system when starting from only 3-OAcpy, which undergoes the partial hydrolysis into 3-OHpy (Scheme 1). 72 Exploration of such in situ ligand transformation has been already introduced in the area of functional molecular materials, especially in the synthesis of coordination clusters. 73−75 Using this unusual approach, which could be not simply reconstructed using the mixture of organic ligands as starting precursors, we achieved the coordination system with both 3-OAcpy and 3-OHpy.…”

“…By checking a number of pyridine derivatives, we found that two closely related ligands, 3-acetoxypyridine (3-OAcpy) and 3-hydroxypyridine (3-OHpy), could appear simultaneously in the aqueous solution of Fe II (3-OAcpy)–[M­(CN) 8 ] n − system when starting from only 3-OAcpy, which undergoes the partial hydrolysis into 3-OHpy (Scheme ). Exploration of such in situ ligand transformation has been already introduced in the area of functional molecular materials, especially in the synthesis of coordination clusters. − Using this unusual approach, which could be not simply reconstructed using the mixture of organic ligands as starting precursors, we achieved the coordination system with both 3-OAcpy and 3-OHpy. Thus, we report the nontrivial synthetic route, crystal structure, and magnetic and optical properties of two isostructural 3-D {Fe II 2 (3-OAcpy) 5 (3-OHpy) 3 [M IV (CN) 8 ]}· n H 2 O (M = Mo, n = 0, FeMo ; M = Nb, n = 1, FeNb ) cyanido-bridged frameworks showing the thermal two-step Fe II SCO effect presented by the temperature-variable structural, magnetic, and spectroscopic studies.…”