Spencer J B, Jordan P M
Department of Biochemistry, University of Southampton, U.K.
Biochem J. 1992 Dec 15;288 ( Pt 3)(Pt 3):839-46. doi: 10.1042/bj2880839.
6-Methylsalicylic acid synthase has been isolated in homogeneous form from Penicillium patulum grown in liquid culture from a spore inoculum. The enzyme is highly susceptible to proteolytic degradation in vivo and in vitro, but may be stabilized during purification by incorporating proteinase inhibitors in the buffers. The enzyme exists as a homotetramer of M(r) 750,000, with a subunit M(r) of 180,000. 6-Methylsalicyclic acid synthase also accepts acetoacetyl-CoA as an alternative starter molecule to acetyl-CoA. The enzyme also catalyses the formation of small amounts of triacetic acid lactone as an oligatory by-product of the reaction. In the absence of NADPH, triacetic acid lactone is the exclusive enzymic product, being formed at 10% of the rate of 6-methylsalicylic acid. The enzyme is inactivated by 1,3-dibromopropan-2-one, leading to the formation of cross-linked dimers similar to that observed with type I fatty acid synthases. Acetyl-CoA protects the enzyme against the inactivation and inhibits dimer formation. An adaptation of the purification method for 6-methylsalicylic acid synthase may be used for the isolation of fatty acid sythase from Penicillium patulum.
已从孢子接种的液体培养物中生长的展青霉中以均一形式分离出6-甲基水杨酸合酶。该酶在体内和体外极易受到蛋白水解降解，但在纯化过程中，通过在缓冲液中加入蛋白酶抑制剂可使其稳定。该酶以分子量为750,000的同四聚体形式存在，亚基分子量为180,000。6-甲基水杨酸合酶也接受乙酰乙酰辅酶A作为乙酰辅酶A的替代起始分子。该酶还催化形成少量的三乙酸内酯作为反应的必然副产物。在没有NADPH的情况下，三乙酸内酯是唯一的酶促产物，其形成速率为6-甲基水杨酸的10%。该酶被1,3-二溴丙酮-2-酮灭活，导致形成与I型脂肪酸合酶类似的交联二聚体。乙酰辅酶A可保护该酶不被灭活并抑制二聚体形成。6-甲基水杨酸合酶纯化方法的一种改进可用于从展青霉中分离脂肪酸合酶。
