Bethin K E, Petrovic N, Ettinger M J
Department of Biochemistry, State University of New York at Buffalo 14214, USA.
J Biol Chem. 1995 Sep 1;270(35):20698-702. doi: 10.1074/jbc.270.35.20698.
The properties of a mouse liver copper binding protein (CuBP) and human placental S-adenosylhomocysteine hydrolase (SAHH) were compared to test the hypothesis that CuBP is SAHH. CuBP and SAHH migrated identically on SDS-polyacrylamide gel electrophoresis gels, and their 48-kDa monomers both self-associate to tetramers. Human placental SAHH cross-reacted with polyclonal antibodies to mouse liver CuBP, and CuBP from mouse liver cross-reacted with two monoclonal antibodies to human placental SAHH. A third monoclonal antibody to human placenta SAHH reacted weakly with the mouse liver protein but well with CuBP from human lymphoblasts. NAD(+)-activated CuBP has high SAHH enzymatic activity. Moreover, human placental SAHH, like mouse liver CuBP, has a single high affinity copper binding site per 48-kDa subunit. Thus, the data confirm that CuBP is SAHH, and SAHH is proposed to be a bifunctional protein with roles in sulfur-amino acid metabolism and copper metabolism. The copper binding activity of SAHH is proposed to play a significant role in the intracellular distribution of copper, and SAHH enzymatic activity may influence copper metabolism through its role in cysteine biosynthesis from methionine.
比较了小鼠肝脏铜结合蛋白（CuBP）和人胎盘S-腺苷同型半胱氨酸水解酶（SAHH）的特性，以检验CuBP就是SAHH这一假说。CuBP和SAHH在SDS-聚丙烯酰胺凝胶电泳凝胶上迁移情况相同，它们48 kDa的单体均能自缔合形成四聚体。人胎盘SAHH与针对小鼠肝脏CuBP的多克隆抗体发生交叉反应，而小鼠肝脏的CuBP与针对人胎盘SAHH的两种单克隆抗体发生交叉反应。针对人胎盘SAHH的第三种单克隆抗体与小鼠肝脏蛋白反应较弱，但与人淋巴母细胞的CuBP反应良好。NAD(+)激活的CuBP具有较高的SAHH酶活性。此外，人胎盘SAHH像小鼠肝脏CuBP一样，每个48 kDa亚基有一个高亲和力铜结合位点。因此，数据证实CuBP就是SAHH，并且SAHH被认为是一种双功能蛋白，在硫氨基酸代谢和铜代谢中发挥作用。SAHH的铜结合活性被认为在铜的细胞内分布中起重要作用，并且SAHH酶活性可能通过其在由甲硫氨酸生物合成半胱氨酸中的作用影响铜代谢。
