Gottlieb L D, Greve L C
Biochem Genet. 1981 Feb;19(1-2):155-72. doi: 10.1007/BF00486145.
The structural gene locus specifying subunits of cytoplasmic isoenzymes of phosphoglucose isomerase (PGI) is present in duplicate in many diploid species of Clarkia (Onagraceae), a genus of annual plants native to California. We studied the kinetic properties and molecular weights of a large number of genetically defined and highly purified PGIs in C. xantiana, a number of species with the duplication, as a means of examining the biochemical consequences of the evolution of a new gene locus. This species is primarily outcrossing, but also includes several previously described predominantly self-pollinating populations. Both cytoplasmic PGI loci in the outcrossing populations are polymorphic and their enzyme products are readily separated by electrophoresis. The PGIs from the outcrossing populations were rated by electrophoresis. The PGIs from the outcrossing populations were generally closely similar in molecular weight, pH optimum, heat sensitivity, energy activation, and apparent Km (fructose-6-phosphate). The PGI loci in the selfing populations are monomorphic and specify enzymes having identical electrophoretic mobilities to those coded by the most frequent alleles of the outcrosser. The PGI isozymes in the selfers differed fivefold in Km, suggesting that they have a very different catalytic effectiveness. The high Km of the PGI-3A' isozyme (1.1mM) was anomalous among the PGIs examined and would likely be disadvantageous in a species which lacked other more normally functioning PGIs. But in the cytoplasm of the selfing plants, it is present with other PGIs that have low Km values. The PGI-3A' enzyme is a good candidate for a gene product coded by a "forbidden" mutation that could not have been established in the absence of the duplication. The rationale for this suggestion is described and it is also pointed out that the divergence of duplicated genes is influenced by many factors such as the breeding system and other population factors as well as the effect of particular mutations.
磷酸葡萄糖异构酶（PGI）细胞质同工酶亚基的结构基因座在Clarkia（柳叶菜科）的许多二倍体物种中是重复存在的，Clarkia是一种原产于加利福尼亚的一年生植物属。我们研究了黄花Clarkia（C. xantiana）中大量经遗传定义且高度纯化的PGI的动力学特性和分子量，黄花Clarkia是具有该重复基因座的多个物种之一，以此作为研究新基因座进化的生化后果的一种手段。该物种主要进行异花授粉，但也包括几个先前描述的主要进行自花授粉的种群。异花授粉种群中的两个细胞质PGI基因座都是多态的，并且它们的酶产物很容易通过电泳分离。对异花授粉种群的PGI进行了电泳分析。异花授粉种群的PGI在分子量、最适pH、热敏感性、能量激活以及表观Km（6-磷酸果糖）方面通常非常相似。自花授粉种群中的PGI基因座是单态的，所指定的酶与异花授粉者最常见等位基因编码的酶具有相同的电泳迁移率。自花授粉植物中的PGI同工酶在Km上相差五倍，这表明它们具有非常不同的催化效率。PGI - 3A'同工酶的高Km值（1.1mM）在所检测的PGI中是异常的，并且在缺乏其他功能更正常的PGI的物种中可能是不利的。但是在自花授粉植物的细胞质中，它与其他具有低Km值的PGI一起存在。PGI - 3A'酶很可能是由一个“禁止”突变编码的基因产物，在没有基因重复的情况下该突变无法确立。文中描述了这一推测的基本原理，并且还指出重复基因的分歧受到许多因素的影响，如繁殖系统和其他种群因素以及特定突变的影响。
