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Inhibiting the Activity of Calf Pregastric Lipase: Effect of Bile Salts, Lecithin, Liposomes, Phenyl Boronic Acid and Diethyl 4-Nitrophenyl Phosphate

Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand

Robyn D. Manuel

Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand

A commercial extract from oropharyngeal tissue of calves has been used as the source of partially purified pregastric lipase. Activity of the enzyme against 4-nitrophenyldecanoate was inhibited by the conjugated bile salts taurocholate, taurodeoxycholate, and tauro- and glyco-chenodeoxycholate in their monomeric form. Although solutions of l--lecithin (0-0.75 mg mL^–1) enhanced the activity of the lipase at all concentrations studied, with maximum rate enhancement (~190%) occurring within the range (0.11-0.34) mg mL^–1, even this concentration of l--lecithin could not remove the inhibitory effect of the bile salts. The Michaelis-Menten parameters, V and K_M, were determined for the activity of the enzyme against 4-nitrophenylacetate in the absence and presence of egg phosphatidylcholine (egg-PC) and egg-PC:cholesterol (10:1 mol/mol) liposomes. While values of V decreased slightly (and to the same extent) in the liposomal suspensions, the value of K_M was decreased by 50% in the normal liposome but increased by 30% in the cholesterol impregnated liposome. The phenyl boronic acid / lipase dissociation constant was evaluated as 1.9 mM and pronounced inhibition was obtained in the presence of diethyl 4-nitrophenyl phosphate (E600). These inhibition results confirmed the presence of serine in the active site of calf pregastric lipase.

Journal of Bioactive and Compatible Polymers, Vol. 15, No. 6, 489-502 (2000)
DOI: 10.1106/RQR1-6VBA-F70W-80KF


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