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Bile salt roles in bile-salt-stimulated lipase activity.

Journal of pediatric gastroenterology and nutrition (1986-07-01)
C J O'Connor, P Walde, R G Wallace
ABSTRACT

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.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Phenyl salicylate, ReagentPlus®, 99%
Sigma-Aldrich
Phenyl salicylate, ≥99%, FG
Supelco
Phenyl salicylate melting point standard, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
Mettler-Toledo Calibration substance ME 30034252, Phenyl salicylate, traceable to primary standards