Stanley J C, Salter M, Fisher M J, Pogson C I
Arch Biochem Biophys. 1985 Aug 1;240(2):792-800. doi: 10.1016/0003-9861(85)90088-8.
The total activity of three key enzymes and the flux through eight steps of aromatic amino acid metabolism have been determined in liver cells isolated from rats fed either control or pyridoxine-free diet for 5-6 weeks. The pyridoxine-free diet caused a decrease in the catabolism of tyrosine and phenylalanine because of a drop in the flux through tyrosine aminotransferase. This decrease of expressed cellular tyrosine aminotransferase activity can be fully explained in terms of loss of cofactor. Larger decreases in the catabolism of tryptophan were seen after pyridoxine deprivation. The decreased extent of tryptophan catabolism can be solely attributed to loss of cofactor or increased degradation of kynureninase. Inhibition of tryptophan 2,3-dioxygenase was seen in pyridoxine deficiency, probably because of the buildup of the kynurenine metabolites. The control strength of kynureninase, for flux through kynureninase, was calculated to be less than or equal to 0.004, but 0.41 after pyridoxine deprivation. The sensitivity of the three pathways to pyridoxine deprivation is interpreted and discussed in terms of the different affinities for pyridoxal phosphate and the control strengths of the pyridoxal phosphate-dependent enzymes, tyrosine aminotransferase and kynureninase.
在从喂食对照饮食或无维生素B6饮食5 - 6周的大鼠分离出的肝细胞中，测定了三种关键酶的总活性以及芳香族氨基酸代谢八个步骤的通量。无维生素B6饮食导致酪氨酸和苯丙氨酸分解代谢减少，这是由于通过酪氨酸转氨酶的通量下降所致。表达的细胞酪氨酸转氨酶活性的这种降低可以完全用辅因子的丧失来解释。维生素B6缺乏后，色氨酸分解代谢的下降幅度更大。色氨酸分解代谢降低的程度可完全归因于辅因子的丧失或犬尿氨酸酶降解的增加。在维生素B6缺乏时观察到色氨酸2,3 - 双加氧酶受到抑制，这可能是由于犬尿氨酸代谢产物的积累。犬尿氨酸酶对通过犬尿氨酸酶的通量的控制强度经计算小于或等于0.004，但在维生素B6缺乏后为0.41。根据对磷酸吡哆醛的不同亲和力以及磷酸吡哆醛依赖性酶酪氨酸转氨酶和犬尿氨酸酶的控制强度，对这三条途径对维生素B6缺乏的敏感性进行了解释和讨论。
