Rothermel B A, Nelson T
Biology Department, Yale University, New Haven, Connecticut 06511.
J Biol Chem. 1989 Nov 25;264(33):19587-92.
Chloroplast-localized NADP-dependent malic enzyme (EC 1.1.1.40) (NADP-ME) provides a key activity for the carbon 4 fixation pathway. In maize, nuclear encoded NADP-ME is synthesized in the cytoplasm as a precursor with a transit peptide that is removed upon transport into the chloroplast stroma. We present here the complete nucleotide sequence for a 2184-base pair full-length maize NADP-ME cDNA. The predicted precursor protein is 636 amino acids long with a Mr of 69,800. There is a strong codon bias found in the amino-terminal portion of NADP-ME that is present in genes for the other enzymes of the C-4 photosynthetic pathway. The NADP-ME transit peptide has general features common to other known chloroplast stroma transit peptides. Comparison of mature maize NADP-ME to the amino acid sequences of known malic enzymes shows two conserved dinucleotide-binding sites. There is a third highly conserved region of unknown function. On the basis of amino acid sequence similarity, the maize chloroplastic enzyme is more closely related to eukaryotic cytosolic isoforms of malic enzyme than to prokaryotic isoforms. We discuss the functional and evolutionary relationship between the chloroplastic and cytosolic forms of NADP-ME.
定位于叶绿体的依赖于NADP的苹果酸酶（EC 1.1.1.40）（NADP-ME）为C4固定途径提供关键活性。在玉米中，核编码的NADP-ME在细胞质中以前体形式合成，带有一个转运肽，该转运肽在转运到叶绿体基质时被去除。我们在此展示了一个2184个碱基对的全长玉米NADP-ME cDNA的完整核苷酸序列。预测的前体蛋白长636个氨基酸，分子量为69,800。在NADP-ME的氨基末端部分发现了强烈的密码子偏好，这种偏好也存在于C4光合途径中其他酶的基因中。NADP-ME转运肽具有与其他已知叶绿体基质转运肽共同的一般特征。将成熟的玉米NADP-ME与已知苹果酸酶的氨基酸序列进行比较，发现了两个保守的二核苷酸结合位点。还有一个功能未知的高度保守的第三个区域。基于氨基酸序列相似性，玉米叶绿体酶与苹果酸酶的真核细胞质同工型比与原核同工型关系更密切。我们讨论了叶绿体和细胞质形式的NADP-ME之间的功能和进化关系。
