Sáez L P, Castillo F, Caballero F J
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba, 14071 Córdoba, Spain.
Curr Microbiol. 1999 Jan;38(1):51-6. doi: 10.1007/pl00006772.
The phototrophic bacterium Rhodobacter capsulatus utilizes the aromatic amino acids L-phenylalanine and L-tyrosine as nitrogen source. L-Phenylalanine is hydroxylated to L-tyrosine, which is further converted into p-hydroxyphenyl pyruvate (pHPP) by a transamination reaction. The bacterium is unable to grow at the expense of these amino acids as the sole carbon source, although it is able to degrade them to homogentisate, probably by unspecific hydroxylation reactions. Metabolization of L-phenylalanine or L-tyrosine as nitrogen source requires phototrophic growth conditions and does not produce free ammonium inside the cells. A low aminotransferase activity with 2-oxoglutarate and L-tyrosine as substrates can be detected in crude extracts of R. capsulatus. Uptake of both amino acids by R. capsulatus was completely inhibited by ammonium addition, which also prevents aminotransferase induction.
光合细菌荚膜红细菌利用芳香族氨基酸L-苯丙氨酸和L-酪氨酸作为氮源。L-苯丙氨酸被羟基化为L-酪氨酸，后者通过转氨反应进一步转化为对羟基苯丙酮酸（pHPP）。尽管该细菌能够通过非特异性羟基化反应将这些氨基酸降解为尿黑酸，但它无法以这些氨基酸作为唯一碳源生长。将L-苯丙氨酸或L-酪氨酸作为氮源进行代谢需要光合生长条件，且不会在细胞内产生游离铵。在荚膜红细菌的粗提物中可以检测到以2-氧代戊二酸和L-酪氨酸为底物时较低的转氨酶活性。添加铵会完全抑制荚膜红细菌对这两种氨基酸的摄取，这也会阻止转氨酶的诱导。
