Serine base-exchange in rat liver nuclei

It has been shown that the incorporation of [C-14]serine into phosphatidyls erine (PS) in isolated rat liver nuclei is intrinsic to this organelle as a ttested by marker enzyme activity. Serine incorporation into PS was the hig hest in nuclei depleted of the outer membrane of the nuclear envelope (nucl eoplasts) and negligible in the outer membrane. Trypsin treatment of nucleo plasts caused a strong inactivation of PS synthesis and only a moderate one of the NAD pyrophosphorylase activity, the marker enzyme of the inner nucl ear membrane. We suggest that the serine base-exchange enzyme is located in the inner membrane of the nuclear envelope and accessible from the peripla smic surface of this membrane. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.