Functional organization of mammalian hexokinase II - Retention of catalytic and regulatory functions in both the NH2- and COOH-terminal halves
Functional organization of mammalian hexokinase II - Retention of catalytic and regulatory functions in both the NH2- and COOH-terminal halves
复制标题
DOI：
10.1074/jbc.271.4.1849
复制
发表时间：
1996-01-26
影响因子：
4.8
通讯作者：
Granner, DK
中科院分区：
文献类型：
--
作者：
Ardehali, H;Yano, Y;Granner, DK
哺乳动物己糖激酶（HK）家族包括三种密切相关的100 kDa亚型（HKI-III），它们被认为是通过基因复制和串联连接从共同的50 kDa前体产生的。HKI的先前研究表明，葡萄糖B-磷酸（Glu-6-P）调节的催化位点位于分子的COOH-末端的一半，而NH 2-末端的一半仅包含Glu-6-P结合位点。相比之下，我们现在表明，代表人类和大鼠HKII的一半的蛋白质具有催化活性，并且每个都被Glu-6-P抑制。完整的酶和酶的NH 2和COOH-末端的一半，每个增加葡萄糖利用率时，在非洲爪蟾卵母细胞中表达。在完整酶中对应于Asp-209或Asp-657的突变分别完全取代NH 2-和COOH-末端半酶。这些位点中的任一个的突变导致100-kDa酶的活性降低50%。两个位点的突变导致活性完全丧失。这表明HKII分子的每一半在100-kDa蛋白质内保留催化活性。这些观察结果表明，HKI和HKII在功能上是不同的，并且进化方式也不同。
The mammalian hexokinase (HK) family includes three closely related 100-kDa isoforms (HKI-III) that are thought to have arisen from a common 50-kDa precursor by gene duplication and tandem ligation. Previous studies of HKI indicated that a glucose B-phosphate (Glu-6-P)-regulated catalytic site resides in the COOH-terminal half of the molecule and that the NH2-terminal half contains only a Glu-6-P binding site. In contrast, we now show that proteins representing both halves of human and rat HKII have catalytic activity and that each is inhibited by Glu-6-P. The intact enzyme and the NH2 and COOH-terminal halves of the enzyme each increase glucose utilization when expressed in Xenopus oocytes. Mutations corresponding to either Asp-209 or Asp-657 in the intact enzyme completely inactivate the NH2- and COOH-terminal half enzymes, respectively. Mutation of either of these sites results in a 50% reduction of activity in the 100-kDa enzyme. Mutation of both sites results in a complete loss of activity. This suggests that each half of the HKII molecule retains catalytic activity within the 100-kDa protein. These observations indicate that HKI and HKII are functionally distinct and have evolved differently.