ABSTRACT
An
O
-acetylserine sulfhydrylase (OASS) from the hyperthermophilic archaeon
Aeropyrum pernix
K1, which shares the pyridoxal 5′-phosphate binding motif with both OASS and cystathionine β-synthase (CBS), was cloned and expressed by using
Escherichia coli
Rosetta(DE3). The purified protein was a dimer and contained pyridoxal 5′-phosphate. It was shown to be an enzyme with CBS activity as well as OASS activity in vitro. The enzyme retained 90% of its activity after a 6-h incubation at 100°C. In the
O
-acetyl-
l
-serine sulfhydrylation reaction, it had a pH optimum of 6.7, apparent
K
m
values for
O
-acetyl-
l
-serine and sulfide of 28 and below 0.2 mM, respectively, and a rate constant of 202 s
−1
. In the
l
-cystathionine synthetic reaction, it showed a broad pH optimum in the range of 8.1 to 8.8, apparent
K
m
values for
l
-serine and
l
-homocysteine of 8 and 0.51 mM, respectively, and a rate constant of 0.7 s
−1
.
A. pernix
OASS has a high activity in the
l
-cysteine desulfurization reaction, which produces sulfide and
S
-(2,3-hydroxy-4-thiobutyl)-
l
-cysteine from
l
-cysteine and dithiothreitol.
摘要
一
O
-乙酰丝氨酸巯基酶 (OASS)
Aeropyrum pernix
K1 与 OASS 和胱硫醚 β-合成酶(CBS)共享吡哆醛 5′-磷酸结合基团。
大肠杆菌
Rosetta(DE3)进行了克隆和表达。纯化的蛋白质为二聚体,含有 5′-磷酸吡哆醛。体外实验表明,它是一种具有 CBS 活性和 OASS 活性的酶。在 100 摄氏度下培养 6 小时后,该酶仍能保持 90% 的活性。在
O
-乙酰-
l
-丝氨酸巯基化反应中,它的最适 pH 值为 6.7,明显的
K
m
值为
O
-乙酰基
l
-丝氨酸和硫化物的值分别为 28 毫摩尔和低于 0.2 毫摩尔,速率常数为 202 秒
-1
.在
l
在 l-胞嘧啶合成反应中,它在 8.1 至 8.8 范围内显示出广泛的 pH 最适值,明显的
K
m
值为
l
-丝氨酸和
l
-和 0.51 mM,速率常数为 0.7 s
-1
.
A. pernix
OASS 在
l
-半胱氨酸脱硫反应中具有很高的活性,该反应产生硫化物和
S
-(2,3-hydroxy-4-thiobutyl)-
l
-从
l
-半胱氨酸和二硫苏糖醇。