Harpster M H, Taylor W C
J Biol Chem. 1986 May 5;261(13):6132-6.
The isozymic forms of maize phosphoenolpyruvate carboxylase (P-enolpyruvate carboxylase) involved in photosynthetic CO2 fixation were shown by protein gel blot analysis to consist of 100-kDa subunits. The nonautotrophic isoform found in roots is comprised of 96-kDa subunits and is about 50-100-fold less prevalent. Further analysis of P-enolpyruvate carboxylase isoforms made use of cloned cDNA probes. Two cDNA clones were isolated from a library constructed from maize leaf poly(A) RNA. The largest clone was complementary to about 25% of P-enolpyruvate carboxylase mRNA, which is 3.4 kilobases in length. The quantity of P-enolpyruvate carboxylase mRNA in green, mature leaf tissue was estimated to be 0.20% of poly(A) RNA, whereas P-enolpyruvate carboxylase mRNA in roots was about 100-fold less prevalent. We used thermal denaturation of a P-enolpyruvate carboxylase cDNA probe hybridized to RNA gel blots to estimate the degree of sequence difference between mRNAs encoding different P-enolpyruvate carboxylase isoforms. There appear to be at least two prevalent P-enolpyruvate carboxylase mRNAs in green leaves which are significantly different in sequence, as are P-enolpyruvate carboxylase mRNAs in roots and shoots. The hybridization pattern of maize genomic DNA Southern blots indicates that P-enolpyruvate carboxylase is encoded by a small gene family.
通过蛋白质凝胶印迹分析表明，参与光合作用中二氧化碳固定的玉米磷酸烯醇式丙酮酸羧化酶（P - 烯醇式丙酮酸羧化酶）的同工酶形式由100 kDa的亚基组成。在根中发现的非自养同工型由96 kDa的亚基组成，其丰度约低50 - 100倍。对P - 烯醇式丙酮酸羧化酶同工型的进一步分析利用了克隆的cDNA探针。从由玉米叶片poly(A) RNA构建的文库中分离出两个cDNA克隆。最大的克隆与约25%的P - 烯醇式丙酮酸羧化酶mRNA互补，该mRNA长度为3.4千碱基。绿色成熟叶片组织中P - 烯醇式丙酮酸羧化酶mRNA的量估计为poly(A) RNA的0.20%，而根中P - 烯醇式丙酮酸羧化酶mRNA的丰度约低100倍。我们利用与RNA凝胶印迹杂交的P - 烯醇式丙酮酸羧化酶cDNA探针的热变性来估计编码不同P - 烯醇式丙酮酸羧化酶同工型的mRNA之间的序列差异程度。绿叶中似乎至少有两种普遍存在的P - 烯醇式丙酮酸羧化酶mRNA，其序列有显著差异，根和茎中的P - 烯醇式丙酮酸羧化酶mRNA也是如此。玉米基因组DNA Southern印迹的杂交模式表明，P - 烯醇式丙酮酸羧化酶由一个小基因家族编码。
