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Human milk bile salt activated lipase ec 3.1.1.3 further characterization and kinetic studies



Human milk bile salt activated lipase ec 3.1.1.3 further characterization and kinetic studies



Journal of Biological Chemistry 256(19): 10198-10202



Further studies on human milk bile salt-activated lipase were performed to provide kinetic and additional chemical characterizations of this enzyme. The enzyme was homogeneous by urea-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and isoelectric focusing with an isoelectric point of 3.7. A unique feature of the amino acid composition of this enzyme was a high proline content (13 mol %). Results of carbohydrate analyses indicated that the enzyme was a glycoprotein containing fucose, galactose, glucosamine, galactosamine and sialic acid. Kinetic studies were performed with various H2O-soluble esters (p-nitrophenyl acetate, 1-monoacetin, 1-monobutyrin and 1-monocaprylin) as substrate and taurocholate as activator. In the presence of a saturating level of taurocholate, the enzyme reaction was demonstrated to follow a rapid equilibrium random uni bi mechanism. These kinetic studies indicated the formation of an enzyme-activator-substrate ternary complex through a random pathway. The mechanism of the activation by taurocholate was due to its enhancement of the binding of the enzyme to the substrate (6.2-fold) and its enhancement of the rate of conversion from enzyme-substrate transitory complex to the products (1.57-fold) when examined with p-nitrophenyl acetate as substrate.

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