核苷二磷酸与三磷酸之间的相互转化
中文名称
通路描述
核苷单磷酸的相互转化由一系列激酶催化，形成核苷二磷酸和三磷酸。核苷单磷酸激酶催化核苷和脱氧核苷5'-单磷酸的可逆磷酸化，形成相应的核苷5'-二磷酸。大多数酶对核苷单磷酸具有特异性限制，并优先使用ATP（Van Rompay et al. 2000; Anderson 1973; Noda 1973）。体内催化这些反应的酶的数量尚不清楚。在六个案例中，已发现纯化蛋白具有明确的生化活性，并在此处进行注释。然而，在分子克隆研究中已鉴定出额外的核苷单磷酸激酶样人类蛋白，其酶活性尚不清楚，并且在细胞提取物中检测到一些独特的核苷单磷酸激酶活性，例如需要GTP的腺苷酸激酶活性（Wilson et al. 1976）和一种或多种鸟苷酸激酶活性（Jamil et al. 1975），这些尚未与特定的人类蛋白明确关联。六个已知特征化的酶所作用的核苷单磷酸底物在表中列出（Van Rompay et al. 2000）。所有六个都优先使用ATP作为磷酸供体，但在体外也具有一些其他核苷三磷酸的活性。体内ATP相对于其他核苷三磷酸的高浓度使得它在大多数条件下可能是这些反应的主要磷酸供体。所有这些磷酸化反应在体外使用纯化的酶和底物时均可自由可逆进行，平衡常数接近1。在体内，ATP与ADP的高比率可能有利于这些反应的正向方向，即(d)NMP和ATP向(d)NDP和ADP的转化。同时，反应的可逆性以及酶底物特异性的重叠使得这一组反应有可能缓冲细胞内的核苷酸池，并调节池中单个核苷酸的相对浓度：如果任何一种分子积累到异常高的水平，似乎有多个途径不仅可用于将其排出，还可用于增加较少丰富核苷酸的供应。核糖核苷还原酶催化从核糖二磷酸合成脱氧核糖二磷酸。
英文描述
Interconversion of nucleotide di- and triphosphates An array of kinases catalyze the reversible phosphorylation of nucleotide monophosphates to form nucleotide diphosphates and triphosphates.Nucleoside monophosphate kinases catalyze the reversible phosphorylation of nucleoside and deoxynucleoside 5'-monophosphates to form the corresponding nucleoside 5'-diphosphates. Most appear to have restricted specificities for nucleoside monophosphates, and to use ATP preferentially (Van Rompay et al. 2000; Anderson 1973; Noda 1973). The total number of human enzymes that catalyze these reactions in vivo is not clear. In six cases, a well-defined biochemical activity has been associated with a purified protein, and these are annotated here. However, additional nucleoside monophosphate kinase-like human proteins have been identified in molecular cloning studies whose enzymatic activities are unknown, and several distinctive nucleoside monophosphate kinase activities detected in cell extracts, e.g., a GTP-requiring adenylate kinase activity (Wilson et al. 1976) and one or more guanylate kinase activities (Jamil et al. 1975) have not been unambiguously associated with specific human proteins.The nucleoside monophosphates against which each of the six well-characterized enzymes is active is shown in the table (Van Rompay et al. 2000). All six efficiently use ATP as a phosphate donor, but have some activity with other nucleoside triphosphates as well in vitro. The high concentrations of ATP relative to other nucleoside triphosphates in vivo makes it the likely major phosphate donor in these reactions under most conditions.All of these phosphorylation reactions are freely reversible in vitro when carried out with purified enzymes and substrates, having equilibrium constants near 1. In vivo, high ratios of ATP to ADP are likely to favor the forward direction of these reactions, i.e., the conversion of (d)NMP and ATP to (d)NDP and ADP. At the same time, the reversibility of the reactions and the overlapping substrate specificities of the enzymes raises the possibility that this group of reactions can buffer the intracellular nucleotide pool and regulate the relative concentrations of individual nucleotides in the pool: if any one molecule builds up to unusually high levels, multiple routes appear to be open not only to dispose of it but to use it to increase the supply of less abundant nucleotides.Ribonucleotide reductase catalyzes the synthesis of deoxyribonucleotide diphosphates from ribonucleotide diphosphates.
所含基因
30 个基因