Abstract
This study was conducted to determine the effect of inhibitors on the kinetics of lipase action in a milk fat system at pH levels of 7 and 8.6. Variations in concentrations of substrate and inhibitors were investigated and results interpreted by means of the Lineweaver-Burk equation. Diisopropyl fluorophosphate (DFP), 2,4-dinitrofluorobenzene (DNFB), and p-hydroxymercuribenzoate (PHMB) ranked in this order in their inhibition effectiveness. Lipase inhibition by PHMB and DFP was greater at pH 8.6 than at pH 7, and the reverse relationship was exhibited by DNFB. Competitive, noncompetitive, and mixed-type inhibition were indicated with these inhibitors, depending upon pH, substrate concentration, and inhibitor concentration. Competitive inhibition was obtained at pH 7 with PHMB and at pH 8.6 with DNFB. At pH 7, noncompetitive inhibition appeared to be obtained with DFP. At pH 8.6 with PHMB, and DFP and at pH 7 with DNFB, partially noncompetitive type or mixed-type inhibition was obtained.Ferric chloride inhibited lipase activity to a greater extent than cupric chloride. Ferric chloride acted as a competitive inhibitor, whereas cupric chloride irreversibly inhibited lipase activity. Inhibition by these metals was uneffected by the pH levels used.
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