Dramatic changes in the activities of squalene-2, 3-epoxide : cycloartenol cyclase and β-amyrin cyclase were observed in germinating pea seeds. By taking advantage of this phenomenon, the two cyclases were purified from pea seedlings. The cyclases were purified to homogeneity by solubilization with Triton X-100, chromatography on hydroxylapatite and diethylaminoethyl (DEAE)-cellulose, isoelectric focusing and gel filtration. Cycloartenol cyclase was purified 471-fold to a specific activity of 167 pkat/mg protein, while β-amyrin cyclase was purified 4290-fold to a specific activity of 28 pkat/mg protein. They each showed a single band on sodium dodecyl sulfate polyacrylamide gel electrophoresis with a molecular mass of 55 and 35 kilodaltons (kDa), respectively. The apparent Km values for (3S)-squalene-2, 3-epoxide were estimated to be 25 and 50 μM, respectively. The cyclases required Triton X-100 or deoxycholate for their highest activity and each showed a broad pH optimum within the range of pH 6.5-7.5. Inhibition by p-chloromercuribenzene sulfonic acid and N-ethylmaleimide suggested involvement of an SH group at the active site of each enzyme.
在发芽的豌豆种子中观察到了鱿烯-2, 3-环氧化酶和β-阿米林环化酶活性发生显著变化。利用这一现象,从豌豆幼芽中纯化了这两种环化酶。通过与Triton X-100溶解、在
羟基磷灰石和二乙
氨基乙基(
DEAE)
纤维素上的层析、电泳聚焦和凝胶滤过,环化酶被纯化到均一性。环化酶纯化了471倍,特异活性为167 pkat/mg 蛋白质,而β-阿米林环化酶纯化了4290倍,特异活性为28 pkat/mg 蛋白质。它们在
十二烷基硫酸钠聚
丙烯酰胺凝胶电泳中各显示出一个单一带,分子质量分别为55和35千道尔顿(kDa)。(3S)-鱿烯-2, 3-
环氧化物的表观Km值估计分别为25和50 μM。这些环化酶需要Triton X-100或脱氧
胆酸以达到最高活性,且各自在pH 6.5-7.5范围内表现出较宽的pH最优值。p-
氯汞苯磺酸和N-乙基马来
酰亚胺的抑制表明,每种酶的活性位点可能涉及一个巯基(SH)。