Zhang J, Blusztajn J K, Zeisel S H
Department of Nutrition, School of Public Health, University of North Carolina, Chapel Hill 27599-7400.
Biochim Biophys Acta. 1992 Oct 27;1117(3):333-9. doi: 10.1016/0304-4165(92)90033-q.
A new assay procedure for measurement of rat liver mitochondrial choline dehydrogenase was developed. Oxidation of [methyl-14C]choline to [methyl-14C]betaine aldehyde and [methyl-14C]betaine was measured after isolating these compounds using HPLC. We observed that NAD+ was required for conversion of betaine aldehyde to betaine in rat liver mitochondria. In the absence of this cofactor, oxidation of choline led to the accumulation of betaine aldehyde. The apparent Km of the mitochondrial choline dehydrogenase for choline was 0.14-0.27 mM, which is significantly lower than previously reported. A partially purified preparation of choline dehydrogenase catalyzed betaine aldehyde formation only in the presence of exogenous electron acceptors (e.g., phenazine methosulfate). This preparation failed to catalyze the formation of betaine even in the presence of NAD+, indicating that betaine aldehyde dehydrogenase may be a separate enzyme from choline dehydrogenase.
开发了一种用于测量大鼠肝脏线粒体胆碱脱氢酶的新检测方法。在使用高效液相色谱法分离出[甲基 - 14C]胆碱、[甲基 - 14C]甜菜碱醛和[甲基 - 14C]甜菜碱后，测量了[甲基 - 14C]胆碱氧化为[甲基 - 14C]甜菜碱醛和[甲基 - 14C]甜菜碱的过程。我们观察到，在大鼠肝脏线粒体中，甜菜碱醛转化为甜菜碱需要NAD +。在没有这种辅因子的情况下，胆碱氧化会导致甜菜碱醛的积累。线粒体胆碱脱氢酶对胆碱的表观Km为0.14 - 0.27 mM，这明显低于先前报道的值。胆碱脱氢酶的部分纯化制剂仅在外源电子受体（如硫酸甲酯吩嗪）存在的情况下催化甜菜碱醛的形成。即使在有NAD +存在的情况下，该制剂也无法催化甜菜碱的形成，这表明甜菜碱醛脱氢酶可能是一种与胆碱脱氢酶不同的酶。
