CATALYTIC PROPERTIES OF TYROSYL RIBONUCLEIC ACID SYNTHETASES FROM ESCHERICHIA COLI AND BACILLUS SUBTILIS
CATALYTIC PROPERTIES OF TYROSYL RIBONUCLEIC ACID SYNTHETASES FROM ESCHERICHIA COLI AND BACILLUS SUBTILIS
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DOI：
10.1021/bi00869a034
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发表时间：
1966-01-01
期刊：
影响因子：
2.9
通讯作者：
BERG, P
中科院分区：
文献类型：
--
作者：
CALENDAR, R;BERG, P
已经制备了来自大肠杆菌和枯草芽孢杆菌的酪氨酰核糖核酸 (RNA) 合成酶的底物特异性的 Acorn-parlson。在四种常见的核糖核苷三磷酸中，只有三磷酸腺苷被两种酶利用。已经检查了 L-酪氨酸结构的几种改变对氨酰腺苷酸形成的影响。除去羧基（酪胺）或其还原（L-酪氨酸）、酰胺化（L-酪氨酸酰胺）或酯化（L-酪氨酸甲酯）会产生无活性的底物，尽管这些类似物都是竞争性抑制剂。 α-氨基（N-乙酰基或N-甘氨酰）的修饰或α-氢被甲基取代产生的化合物既不是底物也不是抑制剂。出乎意料的是，D-酪氨酸被这两种酶激活并转移到 t-RNAtyr。但在每种情况下，与 L-酪氨酸相比，交换反应的 Vmax 较低，Km 较高。将环羟基从 4 位（对位）移动到 3 位（间位）或 2 位（邻位）会产生两种酶均无活性的底物。虽然L-酪氨酸3位上的氯、碘、氨基或硝基取代消除了底物活性，但在相同位置引入氟或羟基后，衍生物仍然具有活性，但Vmax较低，Km较高。苯环转化为吡啶结构（5-羟基-2-(3-DL-丙氨酰)吡啶）使两种酶的 Vmax 降低约一半，Km 增加约 30 倍。枯草芽孢杆菌和大肠杆菌酪氨酰 RNA 合成酶利用任一细菌来源的 t-RNAtyr；两种酶均可形成相同量的酪氨酰 RNA。
Acorn -parlson of the substrate specificity of tyrosyl ribonucleic-acid (RNA) synthetases from E. coll and B. subtilis has been made. Of the four common ribonucleoside triphosphates only adenosine triphosphate is utilized by both enzymes. Several alterations in the L-tyroslne structure have been examined for their effect on the formation of aminoacyl adenylate. Removal of the carboxyl group (tyramine) or its reduction (L-tyrosinol), amidation (L-tyrosine amide), or esterification (L-tyroslne methyl ester) yielded inactive substrates although each of these analogs was a competitive inhibitor. Modification of the a -amino group (N-acetyl or N-glycyl) or substitution of the a hydrogen by a methyl group yielded compounds which were neither substrates nor inhibitors. Quite unexpectedly, D-tyrosine was activated and transferred to t-RNAtyr by both enzymes. But in each case for the exchange reaction the Vmax was lower and the Km was higher than with L-tyrosine. A shift of the ring hydroxyl group from the 4 (para) to the 3 (meta) or 2 (ortho) position yielded inactive substrates with both enzymes. Although substitution of chloro, iodo, amino, or nitro groups in position 3 of L-tyrosine eliminated the substrate activity, after introduction of a fluoro or hydroxy group in the same position the derivatives were still active, but the Vmax was lower and the Km was higher. Conversion of the benzene ring to a pyridine structure (5-hydroxy-2-(3-DL-alanyl) pyridine) decreased the Vmax to about half and increased the Km about 30-fold with both enzymes. The B. subtilis and E. coli tyrosyl RNA synthetases utilize the t-RNAtyr from either bacterial source; the same amount of either tyrosyl RNA is formed with either enzyme.