Save the three entity sets (xhtml-lat1.ent, xhtml-special.ent, and xhtml-symbol.ent)

将这三个实体集（xhtml-lat1.ent、xhtml-special.ent 和 xhtml-symbol.ent）保存到与 DTD 相同的子目录中。

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L-type amino acid transporter-1 (LAT1) is a member of the sodium-independent amino acid transport system L and transports large branched-chain and aromatic neutral amino acids.

哺乳动物氨基酸的跨膜运输由多种氨基酸转运载体蛋白介导，其中L型氨基酸转运载体1（LAT1）属于L系统，主要转运大分子支链氨基酸和芳香族中性氨基酸。

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