The Enzymic Hydrolysis of Phosphatidyl Inositol by Guinea Pig Brain:

Phosphatidylinositol hydrolase activity of homogenates of guinea pig brain was studied by using [2‐ 3 H]inositol labelled substrate and measuring the release of radioactivity into the acid soluble fraction. Inositol phosphate and diglyceride were found to be the main hydrolysis products. The principal enzyme involved, therefore, is a phosphatidylinositol inositolphosphohydrolase. Most of the enzymic activity (61 per cent) was found in the soluble fraction. Osmotic shock of the high speed particulate fraction resulted in release of an additional 23 1 per cent into the soluble fraction. However, as contrasted to lactate dehydrogenase, significant activity remained particulate bound.