Wegman J, Crawford I P
J Bacteriol. 1968 Jun;95(6):2325-35. doi: 10.1128/jb.95.6.2325-2335.1968.
Extracts of Chromobacterium violaceum catalyzed all of the reactions involved in synthesizing tryptophan from chorismic acid. Tryptophan auxotrophs which had lost any of these activities did not produce the characteristic purple pigment, violacein, when grown on a medium in which tryptophan was limiting. Gel filtration of extracts allowed us to estimate molecular weights for the tryptophan enzymes. All of the enzymes appeared to have molecular weights below 100,000. No enzymes were observed to occur in aggregates. The specific activities of the enzymes of the tryptophan pathway did not change when mutants were grown under conditions of limiting or excess tryptophan. The first enzyme in the pathway, anthranilate synthetase, was subject to feedback control by the end product, tryptophan. Tryptophan acted as a noncompetitive inhibitor with respect to glutamine, one of the substrates for anthranilate synthetase, and as a competitive inhibitor of the reaction when chorismate, the other substrate, was varied. The nonlinearity observed in the Lineweaver-Burk plot in the latter case suggests that there may be more than one chorismate-binding site on anthranilate synthetase.
紫色杆菌提取物催化了从分支酸合成色氨酸的所有反应。那些丧失了这些活性中任何一种的色氨酸营养缺陷型菌株，在色氨酸受限的培养基上生长时，不会产生特征性紫色色素——紫菌素。对提取物进行凝胶过滤使我们能够估算出色氨酸合成酶的分子量。所有这些酶的分子量似乎都低于100,000。未观察到酶以聚集体形式存在。当突变体在色氨酸受限或过量的条件下生长时，色氨酸合成途径中酶的比活性没有变化。该途径中的第一种酶——邻氨基苯甲酸合成酶，受终产物色氨酸的反馈控制。色氨酸对邻氨基苯甲酸合成酶的一种底物谷氨酰胺而言，是一种非竞争性抑制剂；当另一种底物分支酸变化时，色氨酸是该反应的竞争性抑制剂。在后一种情况下，Lineweaver - Burk图中观察到的非线性表明，邻氨基苯甲酸合成酶上可能存在不止一个分支酸结合位点。
