Kanayama Y, Dai N, Granot D, Petreikov M, Schaffer A, Bennett A B
Mann Laboratory, Department of Vegetable Crops, University of California, Davis 95616, USA.
Plant Physiol. 1997 Apr;113(4):1379-84. doi: 10.1104/pp.113.4.1379.
Two cDNA clones (Frk1 and Frk2) encoding fructokinase (EC 2.7.1.4) were isolated from tomato (Lycopersicon esculentum). The Frk2 cDNA encoded a deduced protein of 328 amino acids that was more than 90% identical with a previously characterized potato (Solanum tuberosum) fructokinase. In contrast, the Frk1 cDNA encoded a deduced protein of 347 amino acids that shared only 55% amino acid identity with Frk2. Both deduced proteins possessed and ATP-binding motif and putative substrate recognition site sequences identified in bacterial fructokinases. The Frk1 cDNA was expressed in a mutant yeast (Saccharomyces cerevisiae) line, which lacks the ability to phosphorylate glucose and fructose and is unable to grow on glucose or fructose. Mutant cells expressing Frk1 were complemented to grow on fructose but not glucose, indicating that Frk1 phosphorylates fructose but not glucose, and this activity was verified in extracts of transformed yeast. The mRNA corresponding to Frk2 accumulated to high levels in young, developing tomato fruit, whereas the Frk1 mRNA accumulated to higher levels late in fruit development. The results indicate that fructokinase in tomato is encoded by two divergent genes, which exhibit a differential pattern of expression during fruit development.
从番茄（Lycopersicon esculentum）中分离出了两个编码果糖激酶（EC 2.7.1.4）的cDNA克隆（Frk1和Frk2）。Frk2 cDNA编码一个由328个氨基酸组成的推导蛋白，该蛋白与先前鉴定的马铃薯（Solanum tuberosum）果糖激酶的同源性超过90%。相比之下，Frk1 cDNA编码一个由347个氨基酸组成的推导蛋白，它与Frk2的氨基酸同源性仅为55%。这两个推导蛋白都具有在细菌果糖激酶中鉴定出的ATP结合基序和假定的底物识别位点序列。Frk1 cDNA在一个突变酵母（Saccharomyces cerevisiae）品系中表达，该品系缺乏磷酸化葡萄糖和果糖的能力，无法在葡萄糖或果糖上生长。表达Frk1的突变细胞得到互补，能够在果糖上生长，但不能在葡萄糖上生长，这表明Frk1能磷酸化果糖而不能磷酸化葡萄糖，并且在转化酵母的提取物中证实了这种活性。与Frk2对应的mRNA在幼嫩的发育中的番茄果实中积累到高水平，而Frk1 mRNA在果实发育后期积累到更高水平。结果表明，番茄中的果糖激酶由两个不同的基因编码，它们在果实发育过程中表现出不同的表达模式。
