綠膿桿菌色氨酸合成?的活性及調節研究

Abstract

1．大豆苗經1 mM硝酸鈣誘導處理3小時後，硝酸還原酵素活性可達於最高。 2．大豆苗硝酸還原酵素，在標準測定情況下，其最適酸度是7.2；最適溫度是27℃。酵素對受質的Km是4.6×10-4M 3．粗酵素經硫胺沉澱法，磷酸鈣膠法及DEAE-cellulose gel法純化後，可獲17.2倍之純化效果，是遠較Schrader等（1968）所得100倍為小。其原因在繼續追究中。 4．適當濃度之有機含硝基化合物可誘導此酵素的新的合成，惟其誘導機構可能與無機硝酸鹽的誘導者不同。 5．在暗室中生長的大豆苗，Kinetin可刺激酵素的誘導合成作用；Indole-3-Acetic Acid及Gibberellic Acid無影響。光照下生長的大豆苗，外加之植物荷爾蒙時無影響。

Tryptophan synthetase of Pseudomonas aeruginosa, which could catalyze the reaction of indole plus serine to form tryptophan, had a different optimal pH value in different buffer systems. In phosphate buffer system, the optimal pH value was 7.4 and in Tris buffer system, 7.9. The maximum reaction velocity was higher in phosphate buffer than in Tris buffer. The reaction velocity was found to be proportional to incubation time over a period of about twenty minutes, and to the protain concentration in a range of 0 to 600 ug per tube. The enzyme could carry on the reaction at a very low concentration of coenzyme pyridoxal phosphate (1x10-8M). The concentration of substrate serine and indole used in the experiment were 3.7x10-2M and 2.5x10-4 M. At the constant concentration of indole, 2.5x10-4M, the Km for serine was 2.0x10M. and Vmax was 0.66 units. At the constant concentration of serine, 3.7x10-2M, the Km for indole was 1.25x10-3M, and Vmax was 4.0 units, In other words, the concentration of serine used in experiment has reached to the saturation point while that of indole has not. The enzyme level of tryptophan synthetase was repressed by the addition of tryptophan, indole and anthranilate. At the same concentration, 20 ug/ml, indole and anthranilate showed greater repression effect on tryptophan synthetase than tryptophan did, That indole could serve as the growth supplement for the growth of tryptophan auxotroph and reverse the growth inhibition of 6-methyl tryptophan suggested that the repression of indole as due to the conversion of indole to tryptophan. However, that anthranilate showed growth inhibition and repression effect suggested that the repression of anthranilate might not concern with tryptophan. The four analogues used in the experiment, 5-methyl tryptophan, 6-methyl tryptophan, indolepropionic acid and indole acrylic acid, did not have apparent effect on the growth of Pseudomonas aeruginosa. However, they showed repression on enzyme level of tryptophan synthetase when they were added to the growth medium.