Ornithine decarboxylase antizyme - Its structure, role, regulation, and comparative biochemistry

鸟氨酸脱羧酶（ODC）抗酶是一种独特的调节蛋白，参与反馈抑制和可能的酶降解。在第二年的支持研究中获得了以下结果。(1)对新克隆的CDNA和基因组DNA的序列分析表明，大鼠肝脏抗酶MRNA由227个氨基酸组成，抗酶MRNA的翻译可能涉及框移，这在核细胞中是非常罕见的过程。(2)抗酶MRNA的组织分布northern blot分析表明，一种1.3 kb的抗酶MRNA广泛而丰富地分布在小鼠的各种组织中。MRNA在体内相当稳定（T_<1/2> = 12 h），经腐胺处理后其数量没有增加，说明多胺对抗酶的诱导是由于翻译刺激。（Matsufuji）抗酶蛋白合成抑制剂如艾美汀和帕他霉素抑制抗酶合成以及多胺引起的ODC加速衰变，而氨基酸类似物如乙硫氨酸和5-氟色氨酸既不抑制抗酶诱导也不抑制多胺引起的ODC加速衰变，表明这两个过程之间存在密切关系。从odc过量产生的CHO细胞中获得了抗酶过量产生的变异细胞系。对该细胞系中游离ODC和抗酶结合ODC的半衰期的研究强烈提示抗酶介导的ODC降解。(4)抗酶在非洲爪蟾（Xenopus laevus）中的存在及其作用在原代培养的青蛙肝细胞中均观察到抗酶的诱导和ODC的加速衰变。（林&村上）

Ornithine decarboxylase (ODC) antizyme is a unique regulatory protein involved in feedback inhibition and possibly degradation of the enzyme. Following results were obtained in this second year of supported research.(1) Determination of base sequence of antizyme MRNASequence analysis of newly cloned CDNA and genomic DNA indicated that rat liver antizyme is consisted of 227 amino acids and that translation of antizyme MRNA is likely to involve a frame-shift, a very unusual process in bukaryotic cells. (Matsufuji)(2) Tissue distribution of antizyme MRNANorthern blot analysis demonstrated that a single species of antizyme MRNA of 1.3 kb was widely and amply distributed in various murine tissues. The MRNA was quite stable in vivo (T_<1/2> = 12 h) and its amount did not increase upon putrescine treatment, indicating that the induction of antizyme by polyamines is due to translational stimulation. (Matsufuji)Role of antizymeProtein synthesis inhibitors like emetine and pactamycin inhibited antizyme synthesis as well as polyamine-caused acceleration of ODC decay, while amino acid analogs like ethionine and 5-fluorotryptophan inhibited neither antizyme induction nor polyamine-caused acceleration of ODC decay, indicating a close relationship between these two processes. An antizyme overproducing variant cell line was obtained from ODC-overproducing CHO cells. Studies on half-lives of free and antizyme-bound ODC in this cell line strongly suggested antizyme-mediated degradation of ODC. (Murakami)(4) Presence and role of antizyme in the frog Xenopus laevisInduction of antizyme and acceleration of ODC decay were both observed in primary cultured frog hepatocytes. (Hayashi & Murakami)