Materials and Methods

Determination of Phospholipase Activity. When using the classical potentiometric egg yolk assay, designed for pancreatic phospholipases A2 (Nieuwenhuizen et al., 1974), we could not detect any enzymatic activity due to theintestinal phospholipase using different taurodeoxycholate (0-6 mM) or calcium (0-15 mM) concentrations. Similarly, no measurable hy-drolysis was found at pH 8.0 when short-chain dioctanoyl-PC was used at different NaCl concentrations. Due to the sharp substrate specificity of the intestinal phospholipase, we tried to set up a pH stat titration assay using several tissue homogenates or lipid extracts naturally rich in PG or acidic phos-pholipids.

We first checked, without success, Escherichia coli or lamb brain homogenates at pH 8.0 in 21 mM CaCl2 and 1.2 mM taurodeoxycholate. Then we tried, also unsuccessfully, chlo-roform/methanol (2: 1) extracts of E. coli, spinach leaves, and lamb brain as phospholipase substrates as well as purified E. coli PG in the presence of Triton X-100 (1%) or deoxycholate