Recognition of two intracellular cobalamin binding proteins and their identification as methylmalonyl-CoA mutase and methionine synthetase.
Recognition of two intracellular cobalamin binding proteins and their identification as methylmalonyl-CoA mutase and methionine synthetase.
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识别两种细胞内钴胺素结合蛋白并将其鉴定为甲基丙二酸单酰辅酶A变位酶和甲硫氨酸合成酶。
DOI：
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发表时间：
1977
影响因子：
11.1
通讯作者：
R. Allen
中科院分区：
文献类型：
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作者：
J. Kolhouse;R. Allen
粒细胞R型钴胺素结合蛋白将钴胺素（Cbl）专门递送至肝细胞，而转钴胺素II将Cbl递送至各种哺乳动物细胞。两种蛋白质-Cbl复合物均通过胞饮作用进入细胞，并且蛋白质部分在溶酶体中迅速降解。释放的Cbl随后与高分子量细胞内钴胺素结合蛋白（ICB）结合。ICB-Cbl的性质尚不清楚，但似乎很重要，因为ICB-[57 Co]Cbl在一组患者的培养成纤维细胞中缺失，该组患者的细胞正常摄取CN-[57 Co]Cbl，但不将其转化为任何一种辅酶形式。我们检查了超声处理的兔肝的上清液，发现65%的总内源性Cbl以ICB-Cbl形式从Sephadex G-150洗脱，并且该级分还含有两种哺乳动物Cbl依赖性酶，甲基丙二酰-CoA-羰基转移酶（甲基丙二酰-CoA-CoA-羰基转移酶;EC 5.4.99.2）和甲硫氨酸合成酶（四氢蝶酰谷氨酸甲基转移酶; 5-甲基四氢蝶酰-L-谷氨酸：L-高半胱氨酸-S-甲基转移酶; EC 2.1.1.13）。从DEAE-Sephadex梯度洗脱表明，90- 95%的ICB-Cbl用甲基丙二酰辅酶A洗脱，5- 10%用甲硫氨酸合成酶洗脱。静脉注射CN[~（57）Co]Cbl结合粒细胞R型蛋白后2小时，ICB-[~（57）Co]Cbl首次出现。这种ICB-[57 Co]Cbl与甲基丙二酰辅酶A或甲硫氨酸合成酶相关，尽管后者似乎以相对较快的速率形成。我们的研究表明，哺乳动物细胞含有两种ICB，这些蛋白质是甲基丙二酰辅酶A和甲硫氨酸合成酶，并且上述患者组的主要异常在于形成两种Cbl辅酶的共同步骤，并且在Cbl与甲基丙二酰辅酶A和甲硫氨酸合成酶稳定结合之前。
The granulocyte R-type cobalamin binding protein delivers cobalamin (Cbl) exclusively to hepatocytes, and transcobalamin II delivers Cbl to various mammalian cells. Both protein-Cbl complexes enter cells by pinocytosis, and the protein moieties are rapidly degraded in lysosomes. The liberated Cbl is subsequently bound to a high-molecular-weight intracellular cobalamin binding protein (ICB). The nature of ICB-Cbl is unknown but appears important because ICB-[57Co]Cbl is missing from cultured fibroblasts of a group of patients whose cells take up CN-[57Co]Cbl normally but do not convert it to either of its coenzyme forms. We have examined supernatants of sonicated rabbit livers and have found that 65% of the total endogenous Cbl elutes from Sephadex G-150 as ICB-Cbl and that this fraction also contains the two mammalian Cbl-dependent enzymes, methylmalonyl-CoA mutase (methylmalonyl-CoA CoA-carbonylmutase;EC 5.4.99.2) and methionine synthetase (tetrahydropteroylglutamate methyltransferase; 5-methyltetrahydropteroyl-L-glutamate:L-homocysteine-S-methyltransferase; EC 2.1.1.13). Gradient elution from DEAE-Sephadex reveals that 90--95% of the ICB--Cbl elutes with methylmalonyl-CoA mutase and 5--10% elutes with methionine synthetase. ICB--[57Co]Cbl first appears 2 hr after the intravenous injection of CN[57Co]Cbl bound to granulocyte R-type protein. This ICB-[57Co]Cbl is associated with either methylmalonyl-CoA mutase or methionine synthetase although the latter appears to be formed at a relatively faster rate. Our studies indicate that mammalian cells contain two ICBs, that these proteins are methylmalonyl-CoA mutase and methionine synthetase, and that the primary abnormality in the group of patients mentioned above lies at a step that is common to the formation of both Cbl coenzymes and that precedes the stable binding of Cbl to both methylmalonyl-CoA mutase and methionine synthetase.