Callis J, Ho T H
Arch Biochem Biophys. 1983 Jul 1;224(1):224-34. doi: 10.1016/0003-9861(83)90206-0.
A class of plant growth regulators, gibberellins, induce the synthesis of alpha-amylase (1,4-alpha-D-glucan glucanohydrolase, EC 3.2.1.1) in the aleurone layers of barley (Hordeum vulgare L. var. Himalaya) seeds. The purified alpha-amylase is composed of multiple isozymic forms with indistinguishable molecular weights, but different net charges. These alpha-amylase isozymes separate on isoelectric focusing gels into two groups, each containing multiple species. One group has an apparent isoelectric point (pI) of approximately 5.8 (the high pI group). The other group's pI values are around 4.5 (the low pI group). On some gels a small amount of protein focuses between the high and low pI isozymes. These proteins comigrate with the low pI isozymes upon reelectrophoresis. The synthesis of these two groups is temporally regulated. The high pI group is the dominant set of isozymes secreted from embryoless half seeds during the first two days of gibberellin administration. After four days, however, the major isozymes are those of the low pI group. This shift in isozyme pattern is due to a shift in their relative rates of synthesis. Peptide analysis of these two groups of isozymes with Staphylococcus aureus V8 protease and cyanogen bromide shows amino acid sequence differences. However, members within the same group have similar peptide patterns. Both groups of isozymes are synthesized in vitro in a wheat germ extract primed with poly(A)+ RNA isolated from gibberellin-treated aleurone layers. This indicates that the synthesis of the two groups of alpha-amylase isozymes is probably directed by two or more different populations of mature mRNA. A model that explains these observations and the available genetic information is that barley aleurone alpha-amylase isozymes are encoded by at least two sets of structural genes.
一类植物生长调节剂——赤霉素，可诱导大麦（Hordeum vulgare L. var. Himalaya）种子糊粉层中α-淀粉酶（1,4-α-D-葡聚糖葡聚糖水解酶，EC 3.2.1.1）的合成。纯化后的α-淀粉酶由多种同工酶形式组成，它们的分子量难以区分，但净电荷不同。这些α-淀粉酶同工酶在等电聚焦凝胶上可分为两组，每组包含多个种类。一组的表观等电点（pI）约为5.8（高pI组）。另一组的pI值约为4.5（低pI组）。在某些凝胶上，少量蛋白质聚焦于高pI和低pI同工酶之间。重新电泳时，这些蛋白质与低pI同工酶一同迁移。这两组同工酶的合成受到时间调控。在施用赤霉素的前两天，高pI组是无胚半种子分泌的主要同工酶组。然而，四天后，主要同工酶是低pI组的。同工酶模式的这种转变是由于它们相对合成速率的变化。用金黄色葡萄球菌V8蛋白酶和溴化氰对这两组同工酶进行肽分析，结果显示氨基酸序列存在差异。然而，同一组内的成员具有相似的肽模式。两组同工酶均可在体外由用从赤霉素处理的糊粉层中分离的聚腺苷酸加尾RNA（poly(A)+ RNA）引发的小麦胚芽提取物中合成。这表明两组α-淀粉酶同工酶的合成可能由两个或更多不同群体的成熟mRNA指导。一个解释这些观察结果和现有遗传信息的模型是大麦糊粉层α-淀粉酶同工酶由至少两组结构基因编码。
