Determination of phospholipase A2 activity by a colorimetric assay using a pH indicator.

We have set up an assay of phospholipase A2 by a spectrophotometric method, based on the pH change due to the liberation of fatty acids. Among the pH indicators used, phenol red was found to be one of the most sensitive. The activities of different phospholipases A2 from venom and from porcine pancreas were measured by this assay. The results are comparable to those obtained by the pH stat method. This very simple test is rapid, sensitive and especially useful for assaying numerous samples. For quantitative results in absolute units it must be considered that the pH indicator may inhibit some phospholipases.