Strenkoski L F, DeCicco B T
J Bacteriol. 1971 Jan;105(1):296-302. doi: 10.1128/jb.105.1.296-302.1971.
Two amination-deficient mutants of Hydrogenomonas eutropha, characterized by pH-dependent linear growth on non-amino acid substrates, were investigated to determine the exact nature of the mutation. Glutamate dehydrogenase, the only aminating enzyme found in wild-type cells, was present at similar levels in mutant cells. Phenylalanine and aspartate, which allowed normal growth of the mutants, could transaminate 2-oxoglutarate to glutamate, whereas alanine, which does not support normal growth, could not transfer its amino nitrogen to form glutamate. In H. eutropha, l-alanine is apparently synthesized by beta-decarboxylation of aspartate. Studies with NH(4) (+) ions as the sole nitrogen source demonstrated that growth rates of the mutant strains were dependent on both extracellular pH and NH(4) (+) ion concentration. Comparison of these results revealed that the growth rate of mutant cultures was proportional to the concentration of extracellular NH(3). Wild-type cultures were not dependent on extracellular NH(3) since exponential growth rates did not vary with pH or NH(4) (+) ion concentration. The results suggest that the mutant strains lack an NH(4) (+) ion transport system and consequently are dependent on NH(3) diffusion which does not support optimal amination rates. The significance of the findings for the amino acid metabolism of H. eutropha is discussed.
对嗜中性氢单胞菌的两个氨基化缺陷型突变体进行了研究，以确定突变的确切性质，这两个突变体的特征是在非氨基酸底物上呈现pH依赖性线性生长。谷氨酸脱氢酶是野生型细胞中唯一发现的氨基化酶，在突变体细胞中的含量相似。能使突变体正常生长的苯丙氨酸和天冬氨酸可以将2-氧代戊二酸转氨生成谷氨酸，而不能支持正常生长的丙氨酸则不能将其氨基氮转移形成谷氨酸。在嗜中性氢单胞菌中，L-丙氨酸显然是由天冬氨酸的β-脱羧作用合成的。以NH₄⁺离子作为唯一氮源的研究表明，突变菌株的生长速率取决于细胞外pH值和NH₄⁺离子浓度。这些结果的比较表明，突变体培养物的生长速率与细胞外NH₃的浓度成正比。野生型培养物不依赖于细胞外NH₃，因为指数生长速率不会随pH值或NH₄⁺离子浓度而变化。结果表明，突变菌株缺乏NH₄⁺离子转运系统，因此依赖于不支持最佳氨基化速率的NH₃扩散。讨论了这些发现对嗜中性氢单胞菌氨基酸代谢的意义。
