ORNITHINE DECARBOXYLASE MODIFICATION AND INACTIVATION

多胺是真核细胞的重要组成部分。 亚精胺 精胺水平通常与生长速度相关， 在快速生长的胚胎和肿瘤组织中。 的活性 多胺生物合成途径中的限速酶，鸟氨酸 脱羧酶（ODC）在许多不同的反应中迅速变化， 生长条件的变化。 尽管对生物的活动有一定的控制， 这种酶在合成水平上发挥作用，这种酶是最重要的。 不寻常的是，它的周转率远远高于任何其他 真核酶，允许这种酶的极其快速的修饰 活动 然而，人们对这种非常有效的， 特定酶失活机制或其控制。 我们最近的研究 这表明这种快速酶周转可以分为至少两种 阶段。 首先，存在多胺依赖性步骤，其中电荷 酶的特性被轻微修饰，产生可分离的 酶单体的替代形式。 这之后是一个 修饰酶的能量依赖性失活导致最终 降解 我们打算研究鸟氨酸脱羧酶的周转率， 其在体内的控制，该酶的多胺依赖性修饰 以及其随后的能量依赖性失活的机制。 我们 目的是揭示这种特异性的， 非常有效的酶失活。 我们将使用一个大鼠肝癌 细胞系（HTC）及其亚系（HMOA），其在某些点上是缺陷的， 毒品和犯罪问题办公室的交易额 体内研究将涉及受控酶 通过使用亚精胺合成的抑制剂， 甲基乙二醛双（鸟苷酰腙）和二环己胺，以及 代谢能量抑制剂。 拟定的体外研究包括分离 和能量依赖性ODC失活的完整表征。 在 除了阐明这方面的控制最神秘的 酶，这些数据应该特别有助于我们理解 在对致癌物和病毒转化的反应中观察到的ODC活性 正常细胞似乎与这种酶的异常有关 周转

The polyamines are essential components of the eucaryotic cell. Spermidine and spermine levels frequently correlate with growth rate and are elevated in rapidly growing embryonic and neoplastic tissues. The activity of the rate-limiting enzymes in the polyamine biosynthetic pathway, ornithine decarboxylase (ODC), changes quickly in response to many different variations in growth conditions. Athough some control of the activity of this enzyme is exerted at the level of synthesis, this enzyme is most unusual in that it has a turnover rate far greater than any other eucaryotic enzyme, allowing extremely rapid modifications in this enzyme activity. Very little is known, however, about this very efficient, specific enzyme inactivation mechanism or its control. Our recent studies suggest that this rapid enzyme turnover can be separated into at least two phases. First there is a polyamine-dependent step in which the charge characteristics of the enzyme are modified slightly, creating isolatable alternate forms of the enzyme monomer. This is followed by an energy-dependent inactivation of the modified enzyme leading to eventual degradation. We intend to investigate ornithine decarboxylase turnover and its control in vivo, the polyamine-dependent modification of this enzyme and the mechanism of its subsequent energy-dependent inactivation. Our goal is to reveal the mechanisms and control of this specific, and tremendously effective, enzyme deactivation. We will use a rat hepatoma cell line (HTC) and its subline (HMOA) which is deficient at some point in this ODC turnover. In vivo studies will involve controlled enzyme stabilization by use of inhibitors of spermidine synthesis such as methylglyoxal bis (guanylhydrazone) and dicyclohexylamine, as well as metabolic energy inhibitors. Proposed in vitro studies include isolation and complete characterization of the energy-dependent ODC inactivation. In addition to elucidating this facet of the control of a most enigmatic enzyme, these data should specifically help us understand the increase in ODC activity seen in response to carcinogens and viral transformation of normal cells that appear to be related to abnormalities in this enzyme turnover.