Pausch J, Wilkening J, Nowack J, Decker K
Eur J Biochem. 1975 May 6;53(2):349-56. doi: 10.1111/j.1432-1033.1975.tb04075.x.
The site of feedback inhibition of the biosynthesis of pyrimidine nucleotides de novo was investigated in the isolated perfused rat liver. Hepatic uridine phosphate contents were specifically depleted by use of D-galactosamine. The effective activities of enzymes involved in the synthetic pathway were deduced from the rats of incorporation of labeled precursors into the acid-soluble uracil nucleotide pool and into some intermediates of the pathway. The labeling of hepatic urea was also monitored. When the uridine phosphate contents were less than 20% of controls, the incorporation of [14-C]-bicarbonate was stimulated about 20-fold. Label from [U-14C]oxaloacetate used as permeable precursor of intrace-lular aspartate was introduced into the uridylates to the same extent in normal and UTP-depleted livers. Similar results were obtained with labeled carbamoyl phosphate although the uptake of this compound by the liver was rather low. The lack of labeling of urea from exogenous carbamoyl phosphate does not indicate a free exchange of extra- and intramitochondrial carbamoyl phosphate. [ureido-14C]Ureidosuccinate produced in normal and D-galactosamine-treated livers almost identical labeling patterns of dihydroorotate, orotate and orotidine 5'-phosphate. The steady state concentrations of these intermediates were all below 15 nmol/g liver wet weight.
在离体灌注的大鼠肝脏中研究了嘧啶核苷酸从头生物合成的反馈抑制位点。通过使用D-半乳糖胺特异性降低肝脏尿苷磷酸含量。从标记前体掺入酸溶性尿嘧啶核苷酸池和该途径的一些中间体的速率推导出参与合成途径的酶的有效活性。还监测了肝脏尿素的标记情况。当尿苷磷酸含量低于对照的20%时，[14-C] - 碳酸氢盐的掺入受到约20倍的刺激。用作细胞内天冬氨酸可渗透前体的[U-14C]草酰乙酸的标记物在正常肝脏和UTP耗尽的肝脏中以相同程度引入尿苷酸。使用标记的氨甲酰磷酸也获得了类似的结果，尽管肝脏对该化合物的摄取相当低。外源性氨甲酰磷酸未标记尿素并不表明线粒体外和线粒体内氨甲酰磷酸的自由交换。在正常肝脏和D-半乳糖胺处理的肝脏中产生的[ureido-14C]脲基琥珀酸对二氢乳清酸、乳清酸和乳清苷5'-磷酸的标记模式几乎相同。这些中间体的稳态浓度均低于15 nmol/g肝脏湿重。
