NOVEL FEATURES OF PREPHENATE AMINOTRANSFERASE FROM CELL-CULTURES OF NICOTIANA-SILVESTRIS
NOVEL FEATURES OF PREPHENATE AMINOTRANSFERASE FROM CELL-CULTURES OF NICOTIANA-SILVESTRIS
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DOI：
10.1016/0003-9861(85)90161-4
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发表时间：
1985-01-01
影响因子：
3.9
通讯作者：
JENSEN, RA
中科院分区：
文献类型：
--
作者：
BONNER, CA;JENSEN, RA
A prephenate aminotransferase enzyme that produces L-arogenate was demonstrated in extracts from cultured-cell populations of N. silvestris. The enzyme was very active with low concentrations of prephenate, but required high concentrations of phenylpyruvate or 4-hydroxyphenylpyruvate to produce activity levels that were detectable. It is the most specific prephenate aminotransferase described to date from any source. Only L-glutamate and L-aspartate were effective amino-donor substrates. Prephenate concentrations greater than 1 mM produced substrate inhibition, an effect antagonized by increasing concentrations of L-glutamate cosubstrate. The enzyme was stable to storage for at least a month in the presence of pyridoxal 5''-phosphate, EDTA, and glycerol, and exhibited an unusually high temperature optimum of 70.degree. C. The identity of L-arogenate formed during catalysis was verified by high-performance liquid chromatography. DEAE-cellulose chromatography revealed 2 aromatic aminotransferase activities that were distinct from prephenate aminotransferase and which did not require the 3 protectants for stability. The aromatic aminotransferases were active with phenylpyruvate of 4-hydroxyphenylpyruvate as substrates, but not with prephenate. Both of the latter enzymes were similar in substrate specificity, and each exhibited a temperature optimum of 50.degree. C for catalysis. The primary in vivo function of the 2 aromatic aminotransferases is probably to transaminate between the aspartate/2-ketoglutarate and glutamate/oxaloacetate couples, since activities with the latter substrate combinations were an order of magnitude greater than with aromatic substrates. The demonstrated existence of a specific prephenate aminotransferase in N. silvestris meshes with other evidence supporting an important role for L-arogenate in tyrosine and phenylalanine biosynthesis in higher plants.
