Reciprocal Regulation of Ornithine Decarboxylase Degradation by Antizyme and Antizyme Inhibitor.

鸟氨酸脱羧酶（ODC）的细胞水平受其产物腐胺和多胺的负反馈调节。我们之前阐明了多胺诱导的调节蛋白，抗酶（AZ）与ODC结合，使其不稳定。我们还发现了另一种可能的调节蛋白，antizyme inhibitor (AI)，它与ODC大小相似，与AZ结合的亲和力高于ODC。本研究得到以下结果：从大鼠心脏cDNA文库中克隆的AI cDNA序列分析表明，AI是一个由448个氨基酸组成的蛋白，与大鼠ODC高度同源（同源率为47.5%），但与大鼠ODC明显不同，缺乏含有快速降解必需的c端PEST区域。这一结果排除了AI是ODC.2的某种翻译后衍生物的可能性。目前正在对转染后的AI强制表达的效果进行检查，但还没有确切的结果。从非洲爪蟾肝脏中分离出AZ cDNA并测定其序列。青蛙的AZ cDNA与大鼠的AZ cDNA同源性为63%，并且与大鼠的AZ cDNA具有相似的结构，需要多胺诱导的核糖体移框才能翻译。虽然多胺对原生动物四膜虫的ODC有轻微的抑制作用，但ODC的降解速度不受多胺的影响，而且在细胞提取物中没有检测到ODC抑制因子，无论是游离的还是复合的，这表明ODC合成的抑制是多胺对原生动物细胞中ODC抑制的唯一原因。

Cellular level of ornithine decarboxylase (ODC) is under negative feedback regulation by its products putrescine and polyamines. We elucidated previously that polyamine-induced regulatory protein, antizyme (AZ), binds with ODC,destabilizing it. We also found another possible regulatory protein, antizyme inhibitor (AI), which is of similar size with ODC and binds with AZ with higher affinity than ODC.Following results were obtained by the present study.1. Sequence analysis of AI cDNA cloned from rat heart cDNA library revealed that AI is a protein consisting of 448 amino acids, which is highly homologous (47.5 percent identity) to, but clearly distinct from rat ODC,lacking PEST containing C-terminal region essential for rapid degradation. This result excluded the possibility that AI is some post-translational derivative of ODC.2. Examination of the effect of forced expression of transfected AI is under way right now with no firm result yet.3. AZ cDNA was isolated from the liver of Xenopus laevis and its sequence determined. The frog AZ cDNA had 63 percent homology with rat AZ cDNA and had a similar structure with rat cDNA that necessitates polyamine-induced ribosomal frameshifting for its translation. Although polysmines caused mild suppression of ODC in a protozoa Tetrahymena, the rate of ODC degradation was not affected by polyamines and ODC inhibitory factor, of either free or complexed form, was not detected in the cell extract, suggesting that repression of ODC synthesis alone is responsible for the polyamine-caused suppression of ODC in the protozoan cells.