Relationship between tissue levels of S-adenosylmethionine, S-adenylhomocysteine, and transmethylation reactions.
Relationship between tissue levels of S-adenosylmethionine, S-adenylhomocysteine, and transmethylation reactions.
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S-腺苷甲硫氨酸、S-腺苷高半胱氨酸的组织水平与转甲基反应之间的关系。
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发表时间：
1979
期刊：
影响因子：
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通讯作者：
J. A. Duerre
中科院分区：
文献类型：
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作者：
D. Hoffman;W. Cornatzer;J. A. Duerre
本文测定了发育和衰老过程中大鼠大脑、小脑和肝脏中S-腺苷蛋氨酸(ADOMet)、S-腺苷同型半胱氨酸(ADOHcy)和各种甲基转移酶的含量。幼年和成年大鼠肝脏中ADOHcy的含量分别为每克3~7和10~15 nmol。同龄、同性别大鼠肝脏的ADOMet浓度为60~90nmol/g肝脏。它并没有随着年龄的增长而有显著的变化。在出生时，脑组织中ADOMet的浓度为45~50nmol/g，随着器官的成熟，浓度下降到20nmol/g组织中。在大鼠的整个生命周期中，该器官中的ADOHcy水平低于1nmol/g组织。由于ADOMet和ADOHcy的比例相对较高，因此肝脏或脑中组蛋白、DNA或磷脂酰乙醇胺的甲基化速率不会受到ADOHcy的显著影响。在正常营养条件下，ADOMet的组织浓度远高于组蛋白和磷脂酰乙醇胺甲基转移酶的Km值。肝脏和大脑中这些酶的活性水平与细胞内ADOHcy的浓度没有相关性。组蛋白甲基转移酶活性在快速增殖的组织中升高，在没有组蛋白生物合成的情况下明显下降。在肝脏发育过程中，磷脂酰乙醇胺甲基转移酶活性升高。在大鼠脑和肝脏中，ADOHcy水解酶的比活性保持相对恒定。肝脏中该酶的活性是脑中的10倍，而脑中的ADOHcy浓度却低得多。这种化合物的组织水平明显依赖于同型半胱氨酸和腺苷的去除率。腺苷脱氨酶在肝脏和大脑中以相对较高的浓度存在，特别是在发育过程中。
The concentrations of S-adenosylmethionine (AdoMet), S-adenosylhomocysteine (AdoHcy), and various methyltransferases were determined in the cerebrum, cerebellum, and liver of rats during development and aging. The liver contained from 3 to 7 and from 10 to 15 nmol AdoHcy per gram in young and adult rats, respectively. The AdoMet concentration was 60 to 90 nmol/g liver from rats of the same age and sex. It did not vary significantly with age. In the brain the AdoMet concentration was 45 to 50 nmol/g at birth and decreased to 20 nmol/ g tissue with maturity of the organ. The level of AdoHcy in this organ was less than 1 nmol/g tissue throughout the life-span of the rat. Since the ratio of AdoMet to AdoHcy is relatively high, the rate of methylation of histones, DNA, or phosphatidylethanolamine in the liver or brain was not significantly influenced by AdoHcy. Under normal nutritional conditions, the tissue concentration of AdoMet is far above the Km values of histone and phosphatidylethanolamine methyltransferases. The levels of activity of these enzymes in liver and brain did not correlated with the cellular concentration of AdoHcy. Thi histone methyltransferase activity was elevated in rapidly proliferating tissues and declined markedly in the absence of histone biosynthesis. Phosphatidylethanolamine methyltransferase activity was elevated during development of the liver. The specific activity of the AdoHcy hydrolase remained relatively constant in the rat brain and liver. The activity of this enzyme was 10 times higher in liver than in brain, yet the concentration of AdoHcy was much lower in the latter organ. The tissue levels of this compound are evidently dependent on the rates of removal of homocysteine and adenosine. Adenosine deaminase was present in the liver and brain at relatively high concentrations, particularly during development.