CLONING OF ANTIZYME INHIBITOR, A HIGHLY HOMOLOGOUS PROTEIN TO ORNITHINE DECARBOXYLASE

The degradation of ornithine decarboxylase (ODC) catalyzed by the 26 S proteasome is accelerated by antizyme, an ODC inhibitory protein indu ced by polyamines, Previously, we have found another possible regulato ry protein of ODC degradation, antizyme inhibitor, Antizyme inhibitor binds to the antizyme with a higher affinity than that of ODC, releasi ng ODC from ODC-antizyme complex. We report here the cDNA sequence of rat heart antizyme inhibitor, The deduced sequence of the protein is h ighly similar to, but distinct from, sequences of ODCs from various sp ecies, Antizyme inhibitor contains amino acid residues required for fo rmation of active sites of ODC, but it completely lacks ODC activity. Antizyme inhibitor has no homology with pep tide sequence in the mamma lian ODC carboxyl terminus, which is needed for rapid turnover of ODC. It inhibits antizyme-dependent ODC degradation, but, unlike ODC, its degradation is not accelerated by antizyme.