Regulation of Phenylalanine Specific Pathway in a Species of Intrasporangium

Intrasporangium속 방선균의 Phenylalanine 분지대사 경로의 조절

Studies were made on the regulation of chorismate mutase and prephenate dehydratase of a species of Intrasporangium, a phenylalanine producing Actinomycete isolated from soil. Two distinctly regulated species of chorismate mutase, designated CM I and CM IIwere resolved by DEAE Cellulose and DEAE Sephadex A 50 chromatography. The activity of CM II was inhibited by L-tyrosine, whereas that of CM I appeared to be unregulated. Single species of prephenate dehydyatase was also separated in the same purification steps. The activity of the enzyme was strongly feedback inhibited by L-phenylalanine, but by L-tyrosine or L-methionine it was rather slightly stimulated. Synthesis of chorismate mutase was not influenced by the presence of phenylalanine, tyrosine or tryptophan, whereas prephenate dehydratase was found to be subject to strong feedback repression by L-phenylalanine. The rate of repression was 94% at the concentration of 1mM L-phenylalanine but the repression was completely offset by the presence of 5mM tyrosine. The critical regulatory site of the phenylalanine terminal biopathway was, therefore, proved to be the second reaction which was catalyzed by the L-phenylalanine inhibitable and repressible prephenate dehydratase.

토양에서 분리 동정한 phenylalanine 생산균인 Intrasporangium속 방선균의 phenylalanine 생합성 분지경로의 대사조절 특성을 조사하기 위해 chorismate mutase와 prephenate dehydratase를 부분정제한 결과 chorismate mutase는 prephenate dehydratase와 전혀 별개의 단백질로서 두 종의 isoenzyme, chorismate mutase I (CM I)과 chorismate mutase II (CMII)로 구성되어 있음을 알았다. CMI은 최종대사산물인 L-phenylalanine, L-tyrosine 및 L-tryptophan에 대해 완전내성을 보였으나 CMII는 1.5mM tyrosine에 의해서 약 50% 활성 저해를 나타내었다. 이에 비해 prephenate dehydratase는 0.02 mM phenylalanine 존재하에서 95% 이상의 활성 저해를 나타냈으나 이와 같은 L-phenylalanine 활성 저해효과는 positive effector인 L-tyrosine과 L-methionine에 의해 크게 감소되었다. 또한 chorismate mutase 생합성은 feedback repression을 받지 않는데 비해 prephenate dehydratase는 1mM phenylalanine 존재에 의해 약 94%의 효소합성 저해를 나타냈다. 그러나 5mM tyrosine을 동시에 첨가했을 때는 전혀 저해효과를 인식할 수 없었다. 따라서 Intrasporangium속 방선균 역시 대다수의 다른 미생물 균종과 마찬가지로 phenylalanine 분지 경로에서 prephenate dehydratase에 의해 촉매되는 두번째 반응이 가장 중요한 대사조절 단계가 되고 있다는 것을 알 수 있었다.