Ppsa and tkta are the key genes in central metabolism of aromatic amino acids biosynthesis . ppsa encoding phosphoenolpyrucate synthetase a ( ppsa ) which catalyzes pyruvate into pep ; tkta encoding transketolase a which plays a major role in erythrose - 4 - phosphate ( e4p ) production of pentose pathway Ppsa基因编码磷酸烯醇式丙酮酸合成酶a ( ppsa ) ，该酶催化丙酮酸合成磷酸烯醇式丙酮酸； tkta基因编码转酮酶a ，该酶在磷酸戊糖途径中生成4 -磷酸赤藓糖起主要作用。
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So it has increasing commercial demand . escherichia coli and many other microoganism synthesize aromatic amino acids through the condensation reaction between phosphoenolpyru vate ( pep ) and erythrose - 4 - phosphate ( e4p ) to form 3 - deoxy - d - arabinohep tulosonate 7 - phosphate ( dahp ) . pep and e4p are limiting substrates for formation of dahp 大肠杆菌和许多微生物一样，其合成芳香族氨基酸的起始物是由磷酸烯醇式丙酮酸( pep )和4 -磷酸赤癣糖( e4p )二者缩合形成的3 -脱氧- -阿拉伯庚酮糖酸- 7 -磷酸( dahp ) 。
