Purification and Some Properties of Rat Intestinal Ornithine Decarboxylase

Abstract

Ornithine decarboxylase (ODC) was induced in rat small intestine by treatment with hypotonic solution in vitro and purified by two procedures, a conventional procedure and an immunoaffinity procedure. SDS-polyacrylamide gel electrophoresis showed that the molecular weight of the preparation purified by the immunoaffinity procedure (Mr = 53,000) was slightly larger than that of the preparation obtained by the conventional procedure (Mr = 52,000). Values for the Km for L-ornithine (0.1 mM), the isoelectric point (5.4), and the final specific activity (5.1-5.5 x 10(5) nmol CO2/mg protein/30 min) of the two preparations were similar to those reported for the rat liver ODC. Addition of a protease inhibitor (limabean trypsin inhibitor) to the crude extract prevented the appearance of the smaller enzyme (Mr = 52,000) obtained by the conventional purification procedure. Our result indicates that the large enzyme is native ODC and the smaller one is a partial proteolysis product of native ODC.