SOLUBILIZATION OF MEMBRANE ASSOCIATED PHOSPHATIDYLINOSITOL KINASE FROM SACCHAROMYCES CEREVISIAE

Abstract
ATP: phosphatidylinositol (PI) 4-phosphotransferase (PI kinase, EC 2.7.1.67) catalyzes the phosphorylation of PI to form PI 4-monophosphate. A variety of solubilization agents were examined for their ability to release PI kinase from the microsomes of Saccharomyces cerevisiae. The most effective agent to solubilize the enzyme was sodium deoxycholate. Maximal solubilization was obtained with 1% sodium deoxycholate and 10 mM MgCl2. A 2.3-fold increase in specific activity was achieved with 91% of the activity solubilized. The sodium deoxycholate solubilized PI kinase remained at the top of a glycerol gradient whereas the membrane associated enzyme sedimented to the bottom of a glycerol gradient.