EXT1:EXT2 transfers GlcNAc to heparan

Exostosin 1 and 2 (EXT1 and 2) are dual specificity enzymes which catalyze the addition of N-acetylglucosamine (GlcNAc) and glucuronate (GlcA) to the GAG protein linker sequence. The first addition mediated by these enzymes is that of glucuronate after EXTL1 has added the first GlcNAc unit to the linkage sequence. EXT1 and 2 form a heterodimer which translocates to the Golgi apparatus from the ER membrane (McCormick et al. 2000). Defects in EXT1 or 2 cause the hereditary bone disorders multiple exostoses type 1 (MIM:133700) and 2 (MIM:133701) (Wuyts et al. 1998, Bernard et al. 2001).

外源素1和外源素2（EXT1和2）为双特异性酶，催化N-乙酰葡萄糖胺（GlcNAc）和葡萄糖醛酸（GlcA）添加至GAG蛋白连接序列。这些酶介导的第一步添加反应为葡萄糖醛酸，在EXTL1将第一个GlcNAc单元添加至连接序列之后。EXT1和2形成一个异源二聚体，从内质网膜转移到高尔基体（McCormick等人，2000年）。EXT1或2的缺陷会导致遗传性骨病多发性骨疣1型（MIM:133700）和2型（MIM:133701）（Wuyts等人，1998年，Bernard等人，2001年）。