Kohnken R E, Ladror U S, Wang G T, Holzman T F, Miller B E, Krafft G A
Diagnostic Division, Abbott Laboratories, Abbott Park, Illinois 60064, USA.
Exp Neurol. 1995 Jun;133(2):105-12. doi: 10.1006/exnr.1995.1013.
An acid protease activity from human brain was found to cleave a fluorogenic peptide substrate encompassing the amino terminus of Alzheimer's amyloid-beta peptide (A beta). The protease was isolated and determined to be cathepsin D based on chromatographic, immunological, and enzymatic data. Analysis of the cleavage sites indicated that cathepsin D hydrolyzed the methionine--aspartate bond generating the in vivo amino terminus of A beta. These data suggested that cathepsin D could be involved in amyloidogenic processing of the amyloid precursor protein. Consequently, cathepsin D from both Alzheimer's-diseased and control brains was compared to determine whether there were any differences which could account for an increase in A beta production in Alzheimer's disease. No differences were detected in isoform composition or tissue content of cathepsin D as measured by 2-D IEF-SDS-PAGE. Enzymological characterization of brain cathepsin D demonstrated that it could undergo a previously undescribed pH-dependent reversible activation. However, that activation appeared identical for both AD and normal brain enzymes. These data demonstrate that concentration, isoform distribution, and several enzymological characteristics of cathepsin D are not distinguishable between AD and normal brain. The pH dependence of cathepsin D activity suggests, however, that its intracellular localization may be important in considering the potential role of cathepsin D in Alzheimer's disease.
人们发现人脑中的一种酸性蛋白酶活性能够切割一种包含阿尔茨海默病β淀粉样肽（Aβ）氨基末端的荧光肽底物。基于色谱、免疫学和酶学数据，该蛋白酶被分离出来并确定为组织蛋白酶D。对切割位点的分析表明，组织蛋白酶D水解甲硫氨酸-天冬氨酸键，生成Aβ的体内氨基末端。这些数据表明，组织蛋白酶D可能参与淀粉样前体蛋白的淀粉样生成过程。因此，对来自阿尔茨海默病患者大脑和对照大脑的组织蛋白酶D进行了比较，以确定是否存在任何差异，这些差异可以解释阿尔茨海默病中Aβ产生的增加。通过二维IEF-SDS-PAGE测量，未检测到组织蛋白酶D的同工型组成或组织含量存在差异。对脑内组织蛋白酶D的酶学特性进行表征表明，它可能经历一种先前未描述的pH依赖性可逆激活。然而，这种激活在阿尔茨海默病和正常脑酶中看起来是相同的。这些数据表明，组织蛋白酶D的浓度、同工型分布和几种酶学特性在阿尔茨海默病大脑和正常大脑之间无法区分。然而，组织蛋白酶D活性对pH的依赖性表明，在考虑组织蛋白酶D在阿尔茨海默病中的潜在作用时，其细胞内定位可能很重要。
