Fife R S, Moody S, Houser D, Proctor C
Department of Medicine, Indiana University School of Medicine, Indianapolis 46202-5103.
Biochim Biophys Acta. 1994 Sep 28;1201(1):19-22. doi: 10.1016/0304-4165(94)90145-7.
Copper serves as the cofactor for a number of important enzymes in cartilage, as well as in other tissues, including lysyl oxidase, superoxide dismutase, and cytochrome oxidase. Ceruloplasmin is responsible for the transport of approx. 95% of the copper in serum, but the mechanisms for intracellular copper transport are unknown. We have demonstrated recently that a high-molecular-weight cartilage glycoprotein, referred to as CMGP, has regions of sequence homology with ceruloplasmin. CMGP also binds copper and has at least some oxidase activity similar to that of ceruloplasmin. Other tissues synthesize intracellular ceruloplasmin-like proteins. The present report represents part of an effort to examine the hypothesis that CMGP is a copper transport protein in chondrocytes and to characterize the enzymatic activities of CMGP. These studies demonstrate that CMGP is the principal chondrocyte protein labeled by 67Cu in vitro and that the label is localized to the mitochondria, cytosol, and membrane fractions of sucrose gradients, suggesting copper transport through the cell. In parallel experiments, [3H]leucine was incorporated into proteins corresponding to the subunits and fragments of CMGP, as described previously, and in a similar distribution among the subcellular fractions as labeled copper. Additionally, CMGP has oxidase and ferroxidase activities similar to those of ceruloplasmin.
铜是软骨以及其他组织中多种重要酶的辅助因子，这些酶包括赖氨酰氧化酶、超氧化物歧化酶和细胞色素氧化酶。铜蓝蛋白负责血清中约95%的铜的运输，但细胞内铜运输的机制尚不清楚。我们最近证明，一种高分子量软骨糖蛋白，称为CMGP，与铜蓝蛋白具有序列同源区域。CMGP也能结合铜，并且具有至少一些与铜蓝蛋白相似的氧化酶活性。其他组织会合成细胞内类似铜蓝蛋白的蛋白质。本报告是检验CMGP是软骨细胞中一种铜转运蛋白这一假说并对CMGP的酶活性进行表征的部分研究成果。这些研究表明，CMGP是体外被67Cu标记的主要软骨细胞蛋白，且标记物定位于蔗糖梯度的线粒体、胞质溶胶和膜组分中，提示铜在细胞内转运。在平行实验中，[3H]亮氨酸如前所述掺入与CMGP的亚基和片段相对应的蛋白质中，并且在亚细胞组分中的分布与标记铜相似。此外，CMGP具有与铜蓝蛋白相似的氧化酶和铁氧化酶活性。
