Bile salt roles in bile-salt-stimulated lipase activity.
The hydrolysis of 4-nitrophenylacetate and phenylsalicylate, catalyzed by human milk lipase in the presence of a range of concentrations of sodium cholate, has been measured at pH 7.3 and 37.5 degrees C, and maximum activity was observed for both substrates at 1 mmole/dm-3 bile salt. Lineweaver-Burk plots for the enzyme-catalyzed hydrolysis of N-methylindoxyl myristate and 4-nitrophenyloctanoate yielded values of Km equal to 34 and 20 mumoles/dm-3, respectively. However, an increase in the concentration of the latter substrate beyond 10 mumoles/dm-3 was not accompanied by a corresponding increase in the rate of hydrolysis. Comparison of these hydrolysis data with literature data for a variety of hydrophobic substrates suggests that there are two roles for the bile salt in the enzyme-catalyzed reaction--the first involving binding onto several sites on the enzyme, and the second solubilization of oil-phase substrates.
D001647:Bile Acids and Salts / Q000502:physiology*; D001665:Binding Sites; D002384:Catalysis; D004789:Enzyme Activation; D004950:Esterases / Q000032:analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008049:Lipase / Q000378:metabolism*; D008895:Milk, Human / Q000201:enzymology*; D009596:Nitrophenols; D012459:Salicylates; D013379:Substrate Specificity
D001647:Bile Acids and Salts; D009596:Nitrophenols; D012459:Salicylates; C026041:phenyl salicylate; C008642:4-nitrophenyl acetate; D004950:Esterases; D008049:Lipase