From there, four molecules of porphobilinogen condense together to form hydroxymethylbilane with the help of porphobilinogen deaminase.

卟胆原的四个分子一并压缩构成，羟甲基胆素在卟胆原脱氨酶的辅助下。

Note that porphobilinogen deaminase is sometimes called uroporphyrinogen I synthase or hydroxymethylbilane synthase, or HMBS for short.

卟胆原脱氨酶有时被称为尿卟啉原I合成酶或羟甲基胆素合成酶，缩略为HMBS。

Without this enzyme, porphobilinogen cannot be converted to hydroxymethylbilane and the heme synthesis pathway can't continue.

没有了这个酶，卟胆原不能够转化为羟甲基胆素，血红素合成途径中断。