Ekambaram M C, Jernigan H M
Department of Biochemistry, University of Tennessee, Memphis 38163.
Biochim Biophys Acta. 1994 Aug 4;1213(3):289-94. doi: 10.1016/0005-2760(94)00055-7.
In the committed step of phosphatidylcholine and phosphatidylethanolamine synthesis, choline and ethanolamine are phosphorylated to form phosphocholine and phosphoethanolamine. Studies of rat tissues in several laboratories attribute these two kinase activities to a single enzyme for which choline and ethanolamine are competing alternative substrates. However, in this study of intact cultured lenses, choline and ethanolamine were phosphorylated independently, and neither compound inhibited phosphorylation of the other, even at high lenticular concentrations. In contrast, choline kinase in lens homogenates was competitively inhibited by ethanolamine (Ki = 2.3 mM), and choline strongly inhibited ethanolamine kinase activity. The results suggest a fragile metabolic compartmentation or organization of kinase enzyme(s) or substrates within the intact, physiologically integrated lens which results in striking changes in kinetic characteristics when the biological organization of the lens is disrupted.
在磷脂酰胆碱和磷脂酰乙醇胺合成的关键步骤中，胆碱和乙醇胺被磷酸化形成磷酸胆碱和磷酸乙醇胺。多个实验室对大鼠组织的研究将这两种激酶活性归因于一种单一酶，胆碱和乙醇胺是其竞争性替代底物。然而，在这项对完整培养晶状体的研究中，胆碱和乙醇胺是独立被磷酸化的，即使在晶状体中浓度很高时，一种化合物也不会抑制另一种的磷酸化。相反，晶状体匀浆中的胆碱激酶受到乙醇胺的竞争性抑制（Ki = 2.3 mM），胆碱强烈抑制乙醇胺激酶活性。结果表明，在完整的、生理整合的晶状体中，激酶酶或底物存在脆弱的代谢区室化或组织，当晶状体的生物组织被破坏时，会导致动力学特征发生显著变化。
Zotero 插件