O'Brien T G, Madara T, Pyle J A, Holmes M
Proc Natl Acad Sci U S A. 1986 Dec;83(24):9448-52. doi: 10.1073/pnas.83.24.9448.
The properties of ornithine decarboxylase (OrnDCase) from mouse epidermis and benign epidermal tumors (papillomas) induced by the initiation-promotion protocol were compared. When crude extracts from each tissue were incubated at 55 degrees C, epidermal OrnDCase was rapidly inactivated, but the papilloma OrnDCase was more heat stable. Each of five individual papilloma extracts contained OrnDCase activity that was considerably more resistant to heat inactivation than was epidermal OrnDCase. Mixing of a papilloma and epidermal extract produced an intermediate heat-inactivation profile, suggesting that the differences in OrnDCase heat stability are not due to non-OrnDCase components of the extracts. Kinetic analyses indicated that the papilloma OrnDCase has an altered affinity for its substrate, L-ornithine, compared to epidermal OrnDCase. The apparent Km for L-ornithine for the epidermal enzyme was 0.07 mM while the Km values for the individual papilloma OrnDCases clustered around two higher values, 0.3 mM and 1.0 mM. The papilloma OrnDCases, but not epidermal OrnDCase, were activated by GTP and to a lesser extent by CTP. Immunoblot analysis showed the existence of multiple forms of OrnDCase in both epidermis and papilloma that differed in isoelectric point but not subunit molecular weight. None of the species of OrnDCase present in the epidermal extract coincided with the species present in papilloma. These results suggest that one consequence of neoplastic transformation in this in vivo system is the presence of an OrnDCase protein in benign tumors that differs structurally and functionally from the OrnDCase present in normal epidermis. The possible mechanisms responsible for these results and their significance for neoplastic development in this tissue are discussed.
比较了小鼠表皮和由启动-促进方案诱导的良性表皮肿瘤（乳头状瘤）中鸟氨酸脱羧酶（OrnDCase）的特性。当将每个组织的粗提物在55摄氏度下孵育时，表皮OrnDCase迅速失活，但乳头状瘤OrnDCase对热更稳定。五个单独的乳头状瘤提取物中的每一个都含有OrnDCase活性，该活性比表皮OrnDCase对热失活的抵抗力要强得多。将乳头状瘤提取物和表皮提取物混合产生了中间热失活曲线，这表明OrnDCase热稳定性的差异不是由于提取物中的非OrnDCase成分造成的。动力学分析表明，与表皮OrnDCase相比，乳头状瘤OrnDCase对其底物L-鸟氨酸的亲和力发生了改变。表皮酶对L-鸟氨酸的表观Km为0.07 mM，而各个乳头状瘤OrnDCase的Km值集中在两个较高的值附近，即0.3 mM和1.0 mM。乳头状瘤OrnDCase被GTP激活，但不被表皮OrnDCase激活，CTP对其激活程度较小。免疫印迹分析表明，表皮和乳头状瘤中均存在多种形式的OrnDCase，它们的等电点不同，但亚基分子量相同。表皮提取物中存在的OrnDCase种类与乳头状瘤中存在的种类均不相同。这些结果表明，在这个体内系统中肿瘤转化的一个后果是良性肿瘤中存在一种OrnDCase蛋白，其结构和功能与正常表皮中存在的OrnDCase不同。讨论了导致这些结果的可能机制及其对该组织肿瘤发生的意义。
