Forster S, Lloyd J B
Biochim Biophys Acta. 1985 Apr 11;814(2):398-400. doi: 10.1016/0005-2736(85)90461-4.
In the human recessive condition cystinosis, cystine transport has been reported to be normal in the plasma membrane but defective in the lysosome membrane. A possible explanation is that the transport systems at the two cellular sites are identical and that the defect in cystinosis affects the porter's ability to operate at the low pH of the lysosome. To test this hypothesis the uptake of 3H-labelled cystine and glutamate by normal and cystinotic human skin fibroblasts has been measured in vitro at pH 5.8, 6.5, 7.0, 7.4 and 8.0. Uptake of glutamate was more rapid than that of cystine. Uptake of cystine increased with increasing pH, but uptake of glutamate showed no marked pH-dependence. Transport in cystinotic cells was similar to that in normal cells, and similarly affected by pH. This finding is incompatible with the hypothesis proposed above. It is concluded that the cystine porters of the plasma membrane and the lysosome membrane are probably genetically distinct.
在人类隐性疾病胱氨酸病中，据报道胱氨酸转运在质膜中正常，但在溶酶体膜中存在缺陷。一种可能的解释是，这两个细胞部位的转运系统是相同的，而胱氨酸病中的缺陷影响了转运蛋白在溶酶体低pH环境下的运作能力。为了验证这一假设，在体外分别于pH 5.8、6.5、7.0、7.4和8.0条件下，测定了正常人和患胱氨酸病的人皮肤成纤维细胞对3H标记的胱氨酸和谷氨酸的摄取情况。谷氨酸的摄取比胱氨酸更快。胱氨酸的摄取随pH升高而增加，但谷氨酸的摄取没有明显的pH依赖性。胱氨酸病细胞中的转运与正常细胞相似，且同样受pH影响。这一发现与上述假设不相符。结论是，质膜和溶酶体膜的胱氨酸转运蛋白可能在基因上是不同的。
