N-terminal extensions of the human AMPD2 polypeptide influence ATP regulation of isoform L.
N-terminal extensions of the human AMPD2 polypeptide influence ATP regulation of isoform L.
复制标题
人 AMPD2 多肽的 N 端延伸影响亚型 L 的 ATP 调节。
DOI：
10.1016/s0006-291x(03)00787-3
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发表时间：
2003
影响因子：
3.1
通讯作者：
Sabina,RichardL
中科院分区：
文献类型：
--
作者：
Haas,AmyLouise;Sabina,RichardL
人类组织和细胞表达三种AMP脱氨酶（AMPD）亚型，含有不同的N-末端结构域，编码这些酶的多基因家族的每个成员产生替代转录本，通过延伸和盒型取代赋予额外的N-末端分歧。现有的数据表明，不同的N-末端结构域可以影响AMPD亚型的行为，但每个酶内的额外分歧的功能意义是未知的。三种亚型L（AMPD 2）变体1A/2、1B/2和1B/3分别含有47、128和53个氨基酸的N-末端延伸。本研究确定了这三种亚型L酶在阳性（ATP）和阴性（磷酸盐）变构效应物存在下的动力学和调节行为。所有显示几乎相同的动力学参数和调节反应的磷酸盐单独存在下，或与ATP的组合。ATP的调节是双相的，三种同工型L酶在1 mM磷酸盐存在下也表现出相似的激活曲线和2- 3 mM的最大初始速度，而更高浓度的磷酸盐抑制这种激活。然而，在不存在磷酸盐的情况下，在较低的ATP浓度（0.8-1.5mM）下实现最大初始速度，并且在这些条件下，与在非肌肉细胞中发现的ATP浓度范围（0.8-3.7mM）内的1 mM磷酸盐相比，1B/2活性较低，1B/3活性较高，并且1A/2活性相似。这些综合结果表明，同种型L酶被设计为在它们表达的非横纹肌环境中遇到的不同代谢条件下发挥作用。
Human tissues and cells express three AMP deaminase (AMPD) isoforms containing divergent N-terminal domains, and each member of the multigene family encoding these enzymes produces alternative transcripts that confer additional N-terminal divergence through extensions and cassette-type substitutions. Available data suggest that divergent N-terminal domains can influence AMPD isoform behavior, but the functional significance for additional divergence within each enzyme is unknown. Three isoform L (AMPD2) variants, 1A/2, 1B/2, and 1B/3, contain N-terminal extensions of 47, 128, and 53 amino acids, respectively. This study has determined the kinetic and regulatory behaviors of these three isoform L enzymes in the presence of positive (ATP) and negative (phosphate) allosteric effectors. All display nearly identical kinetic parameters and regulatory responses in the presence of phosphate alone, or in combination with ATP. Regulation by ATP is biphasic and the three isoform L enzymes also exhibit similar activation profiles and maximum initial velocities at 2–3mM in the presence of 1mM phosphate, whereas higher concentrations of phosphate suppress this activation. However, maximum initial velocities are achieved at lower ATP concentrations (0.8–1.5mM) in the absence of phosphate and under these conditions 1B/2 is less active, 1B/3 is more active, and 1A/2 is similarly active when compared to 1mM phosphate over the range of ATP concentrations found in non-muscle cells (0.8–3.7mM). These combined results suggest that isoform L enzymes are designed to function under different metabolic conditions encountered in the non-striated muscle environments where they are expressed.