Matchett W H, DeMoss J A
J Biol Chem. 1975 Apr 25;250(8):2941-6.
Tryptophan synthase of Neurospora crassa was purified to electrophoretic homogeneity from the wild type strain 74A which had been derepressed by the presence of 0.5 mM indoleacrylic acid in the growth medium. The isolated material migrated as a single symmetrical peak in the ultracentrifuge with a sedimentation constant of 6.0 S. Gel filtration on Sephadex G-200 AND CONVENTIONAL SEDIMENTATION EQUILIBIRIUM YIELDED MOLECULAR WEIGHT ESTIMATES OF 151,000 PLUS AND MINUS 10,000 AND 149,000 PLUS AND MINUS 10,000, RESPECTIVELY. Treatment of the enzyme with sodium dodecyl sulfate followed by polyacrylamide gel electrophoresis gave a single band with a relative mobility suggesting a molecular weight of 76,000 plus and minus 2000. Aspartic acid was the only detectable NH2-terminal amino acid and experiments with carboxypeptides A and B revealed that the three amino acids, isoleucine, leucine, and phenylalanine, were released rapidly and in the order mentioned. These results are interpreted as indicating that the Neurospora enzyme is a homodimer.
粗糙脉孢菌的色氨酸合成酶是从野生型菌株74A中纯化得到的，该菌株在生长培养基中因存在0.5 mM吲哚丙烯酸而被去阻遏。分离得到的物质在超速离心机中以单一对称峰迁移，沉降常数为6.0 S。在Sephadex G - 200上进行凝胶过滤和常规沉降平衡分别得到分子量估计值为151,000 ± 10,000和149,000 ± 10,000。用十二烷基硫酸钠处理该酶，然后进行聚丙烯酰胺凝胶电泳，得到一条相对迁移率表明分子量为76,000 ± 2000的单一带。天冬氨酸是唯一可检测到的NH2末端氨基酸，用羧肽酶A和B进行的实验表明，异亮氨酸、亮氨酸和苯丙氨酸这三种氨基酸按所述顺序迅速释放。这些结果被解释为表明脉孢菌酶是一种同型二聚体。
