Misset O, Van Beeumen J, Lambeir A M, Van der Meer R, Opperdoes F R
Eur J Biochem. 1987 Feb 2;162(3):501-7. doi: 10.1111/j.1432-1033.1987.tb10668.x.
Trypanosoma brucei contains two glyceraldehyde-phosphate (GAPDH; EC 1.2.1.12) isoenzymes; one is located in glycosomes and represents 80% of the total activity, whereas the other is present in the cytosol. The purification of the cytosolic GAPDH, which is identical in both bloodstream-form and insect-stage trypanosomes, is described, and the enzyme compared with its glycosomal counterpart. Cytosolic GAPDH is specific for NAD. It is a tetrameric enzyme with subunits of 33.5 kDa, 5 kDa smaller than those of the glycosomal GAPDH. The native enzyme has a pI of 7.9, which is 1.5 pH units less basic than the glycosomal enzyme. Both enzymes display maximal activity at pH 8 but the cytosolic enzyme has a much broader activity profile especially towards lower pH values. Sequence comparison of the first 85 amino acids reveals that the N-terminal parts of both isoenzymes differ by 52%. The N terminus of the cytosolic isoenzyme resembles the corresponding N termini of ten other known GAPDH sequences in that they all lack three amino-acid insertions, which so far only have been found in the glycosomal isoenzyme of T. brucei. This observation explains in part the great difference in subunit size between the two T. brucei isoenzymes and suggests that at least one of these insertions is responsible for import of the glycosomal isoenzyme into the organelle.
布氏锥虫含有两种甘油醛 - 3 - 磷酸脱氢酶（GAPDH；EC 1.2.1.12）同工酶；一种位于糖体中，占总活性的80%，而另一种存在于细胞质中。本文描述了细胞质GAPDH的纯化过程，该酶在血流形式和昆虫阶段的锥虫中是相同的，并将其与糖体中的对应酶进行了比较。细胞质GAPDH对NAD具有特异性。它是一种四聚体酶，亚基分子量为33.5 kDa，比糖体GAPDH的亚基小5 kDa。天然酶的pI为7.9，比糖体酶的碱性低1.5个pH单位。两种酶在pH 8时都表现出最大活性，但细胞质酶具有更宽的活性谱，尤其是在较低pH值时。对前85个氨基酸的序列比较表明，两种同工酶的N端部分差异为52%。细胞质同工酶的N端类似于其他十种已知GAPDH序列的相应N端，因为它们都缺少三个氨基酸插入，而到目前为止，这些插入仅在布氏锥虫的糖体同工酶中发现。这一观察结果部分解释了布氏锥虫两种同工酶亚基大小的巨大差异，并表明这些插入中的至少一个负责糖体同工酶导入细胞器。
