Katz B M, Barnea A
Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center, Dallas 75235.
J Biol Chem. 1990 Feb 5;265(4):2017-21.
It has been previously shown that complexation of Cu2+ is essential for effective uptake of Cu2+ by brain tissues and that 67Cu complexed to His is taken up by a high affinity and a low affinity saturable process (Hartter, D. E., and Barnea, A. (1988) J. Biol. Chem. 263, 799-805). Using rat hypothalamic tissue slices, we defined the ligand specificity for these two uptake processes. The effectiveness of stereoisomers or methyl (Me) derivatives of His in facilitating 67Cu uptake by the high affinity process was in this decreasing order: L-His = D-His = Me-3-N-His greater than Me-ester-His greater than Me-alpha-N-His greater than or equal to Me-1-N-His. By the low affinity process it was: L-His = D-His = Me-3-N-His = Me-ester-His = Me-alpha-N-His greater than Me-1-N-His. When facilitation of 67Cu uptake by 14 different amino acids was evaluated using copper:ligand (Cu:L) ratios of 1:2,000 (high affinity process) or 1:2 (low affinity process), His stood out as the most effective. However, when [Cu2+] was 0.1 microM and the Cu:L ratio was increased from 1:2,000 to 1:20,000, Ala, Gly, Lys, Ser, or Thr was each as effective as His; when [Cu2+] was 10 microM and the Cu:L ratio was increased from 1:2 to 1:2,000, Gln, Glu, Gly, Lys, or Ser was each superior to His in facilitating 67Cu uptake. Moreover, by comparison to 67Cu uptake at a Cu:L ratio of 1:2, increasing the ratio attenuated (His) or enhanced (Gln, Glu, Gly, Lys, Ser) 67Cu uptake. These results indicate that 1) coordination of Cu2+ with the 1-N-imidazole and the alpha-amino (but not with the carboxyl) is essential for His facilitation of 67Cu uptake, and 2) the amino acid specificity for uptake of complexed Cu2+ is a function of both [Cu2+] and the molar ratio of copper to amino acid. These results are consistent with coordination of Cu2+ with at least three nitrogens being a primary factor facilitating copper uptake by brain tissue.
先前的研究表明，Cu2+的络合对于脑组织有效摄取Cu2+至关重要，并且与组氨酸络合的67Cu通过高亲和力和低亲和力饱和过程被摄取（哈特特，D.E.，和巴尼亚，A.（1988年）《生物化学杂志》263卷，799 - 805页）。我们使用大鼠下丘脑组织切片，确定了这两种摄取过程的配体特异性。组氨酸的立体异构体或甲基（Me）衍生物促进67Cu通过高亲和力过程摄取的有效性顺序为：L - 组氨酸 = D - 组氨酸 = Me - 3 - N - 组氨酸＞Me - 酯 - 组氨酸＞Me - α - N - 组氨酸≥Me - 1 - N - 组氨酸。通过低亲和力过程，顺序为：L - 组氨酸 = D - 组氨酸 = Me - 3 - N - 组氨酸 = Me - 酯 - 组氨酸 = Me - α - N - 组氨酸＞Me - 1 - N - 组氨酸。当使用铜：配体（Cu:L）比例为1:2000（高亲和力过程）或1:2（低亲和力过程）评估14种不同氨基酸对67Cu摄取的促进作用时，组氨酸是最有效的。然而，当[Cu2+]为0.1微摩尔，且Cu:L比例从1:2000增加到1:20000时，丙氨酸、甘氨酸、赖氨酸、丝氨酸或苏氨酸促进67Cu摄取的效果与组氨酸相同；当[Cu2+]为10微摩尔，且Cu:L比例从1:2增加到1:2000时，谷氨酰胺、谷氨酸、甘氨酸、赖氨酸或丝氨酸在促进67Cu摄取方面均优于组氨酸。此外，与Cu:L比例为1:2时的67Cu摄取相比，增加该比例会减弱（组氨酸）或增强（谷氨酰胺、谷氨酸、甘氨酸、赖氨酸、丝氨酸）67Cu摄取。这些结果表明：1）Cu2+与1 - N - 咪唑和α - 氨基（而非羧基）的配位对于组氨酸促进67Cu摄取至关重要；并且2）络合Cu2+摄取的氨基酸特异性是[Cu2+]以及铜与氨基酸摩尔比的函数。这些结果与Cu2+与至少三个氮原子配位是促进脑组织摄取铜的主要因素这一观点一致。
