Collarini E J, Pisoni R L, Christensen H N
Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor.
Biochim Biophys Acta. 1989 Dec 28;987(2):139-44. doi: 10.1016/0005-2736(89)90536-1.
L-Aspartate and L-glutamate are transported into human fibroblast lysosomes by a single, low Km, Na(+)-independent transport system, which has been provisionally named lysosomal system d. This system resembles the Na(+)-dependent plasma membrane system chi-AG, although these differences have been observed: (1) lysosomal system d recognizes the D- as well as the L-isomers of both aspartate and glutamate, whereas only for aspartate is the D-isomer recognized by system chi-AG; (2) the anion L-homocysteate is not accepted by system chi-AG, but is an effective inhibitor of lysosomal system d; (3) N-methyl, alpha-methyl, and omega-hydroxamate derivatives of both aspartate and glutamate inhibit lysosomal system d, but only the aspartate derivatives are accepted by system chi-AG; (4) lysosomal system d shows a preference for the substrate amino group in the alpha-position, a preference not seen for system chi-AG. These points imply differences at the two recognition sites with respect to substrate length, size, and rotation, with the lysosomal site generally being the less restrictive.
L-天冬氨酸和L-谷氨酸通过一种单一的、低Km值、不依赖Na⁺的转运系统被转运到人类成纤维细胞溶酶体中，该系统暂被命名为溶酶体系统d。这个系统类似于依赖Na⁺的质膜系统χ-AG，不过已观察到以下差异：(1) 溶酶体系统d能识别天冬氨酸和谷氨酸的D型以及L型异构体，而系统χ-AG仅识别天冬氨酸的D型异构体；(2) 阴离子L-高半胱氨酸不被系统χ-AG接受，但却是溶酶体系统d的有效抑制剂；(3) 天冬氨酸和谷氨酸的N-甲基、α-甲基和ω-异羟肟酸酯衍生物抑制溶酶体系统d，但只有天冬氨酸衍生物被系统χ-AG接受；(4) 溶酶体系统d对α位的底物氨基有偏好，系统χ-AG则没有这种偏好。这些要点意味着在两个识别位点上，底物的长度、大小和旋转方面存在差异，溶酶体位点通常限制较少。
