Research for the Inhibitor of Cholesterol Biosynthesis with the aid of Morus alba Callus Cultures

桑树细胞至少有两条类异戊二烯生物合成途径，其中一条是异戊二烯基酚的合成途径，另一条是甾醇的合成途径。在用潜在的3-羟基-3-甲基戊二酰辅酶A(HMG-CoA)还原酶抑制剂--致密蛋白处理白曲霉细胞时，致密蛋白对异戊二烯基苯酚的生物合成没有影响，而对乙酸酯合成β-谷甾醇的异戊二烯单位有抑制作用。这一结果表明，致密蛋白是一种特异性的醋酸来源的甾醇生物合成的抑制物。因此，这项工作表明至少存在两条类异戊二烯生物合成途径，其中一条对致密蛋白敏感，另一条对致密蛋白耐药。在以前用[2-^&lt；13&gt；C]醋酸酯进行的实验中，已经发现三羧酸(TCA)循环参与了白曲霉细胞培养物中异戊二烯基苯酚的生物合成。在[2-^&lt；13&gt；C]乙酸N-乙酰半胱胺硫酸酯的作用下，醋酸酯前体在没有TCA环参与的情况下完整地进入异戊二烯基苯酚单元，另一方面，细胞培养物中的异戊二烯基酚是由肉桂酰聚酮中间体生物合成的。同时给予~&lt；13&gt；C标记的L-苯丙氨酸和L-酪氨酸，以及~&lt；13&gt；标记的肉桂酸N-乙酰半胱氨酸硫酯衍生物同时作用于白曲霉细胞，确证了产生p-香豆酰辅酶A的两条独立途径，一条是L-苯丙氨酸通过肉桂酰辅酶A脱氨生成p-香豆酰辅酶A的途径，另一条是L-酪氨酸通过脱氨反应生成p-香豆酰辅酶A的途径。

Morus alba Cell cultures have at least two isoprenoid biosynthetic pathways, one of which is that for isoprenylated phenols and the other is that for sterols. In the administration of experiment with compactin, a potential 3-hydroxy 3-methylglutaryl CoA (HMG CoA) reductase inhibitor, to the M.alba cell cultures, the biosynthesis of the isoprene unit of the isoprenylated phenol was not affected by compactin, while the biosynthesis of the isoprene unit of beta-sitosterol from acetate was inhibited. This result suggests that compactin is a specific inhibitor of sterol biosynthesis from acetate origin. This work thus indicates the occurrence of at least two isoprenoid biosynthetic pathways, one of which is susceptible to compactin and the other resistant to compactin in M.alba cell cultures. In the previous experiment with [2-^<13>C] acetate, it has been found that the tricarboxylic acid (TCA) cycle participates in the biosynthesis of the isoprene unit of the isoprenylated phenol in M.alba cell cultures. In the administration of [2-^<13>C] acetic acid N-acetylcysteamine thioester to the cell cultures, the acetate precursor was intact into the isoprene unit of the isoprenylated phenol without the participation of the TCA cycle.On the other hand, the isoprenylated phenols in the cell cultures are biosynthesized from cinnamoylpolyketide intermediate. Simultaneous administration of ^<13>C-labeled L-phenylalanine and L-tyrosine as well as administration of ^<13>-labeled cinnamic acid N-acetylcysteamine thioester derivative to the M.alba cell cultures gave a conclusive evidence for the two independent pathways leading to p-coumaroyl CoA.One is pathway from L-phenylalanine to p-coumaroyl CoA by way of cinnamoyl CoA and the other is pathway from L-tyrosine to p-coumaroyl CoA through the deamination reaction.