Sterniczuk A, Hreniuk S, Scaduto R C, LaNoue K F
Department of Physiology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey 17033.
Eur J Biochem. 1991 Feb 26;196(1):143-50. doi: 10.1111/j.1432-1033.1991.tb15797.x.
A kinetic expression for rat-liver mitochondrial aspartate formation in situ was developed in order to determine whether hormonally induced decreases in 2-oxoglutarate levels can regulate hepatic gluconeogenesis from lactate via control of aspartate formation. Previous studies from this laboratory showed that 2-oxoglutarate can inhibit aspartate production by isolated mitochondria. These present studies were designed to probe the physiological significance of the decrease in 2-oxoglutarate levels observed when Ca2(+)-mobilizing gluconeogenic hormones are administered to isolate perfused rat livers. First, estimates were made of the kinetic constants which determine the rate of aspartate formation in isolated mitochondria. The concentrations of the substrates and products of this process were then measured in perfused livers. From these values, it was possible to estimate aspartate efflux from mitochondria in situ. The calculated rates of aspartate production were increased by decreases in 2-oxoglutarate levels which occurred when glucagon or phenylephrine was added to the perfused livers. Glucagon also effected an inhibition of pyruvate kinase, evidenced by the fact that the calculated rate of aspartate efflux equalled the rate of gluconeogenesis (the difference between the two is equivalent to the pyruvate-kinase flux). By contrast, in control livers and with phenylephrine stimulation, aspartate formation was higher than gluconeogenesis suggesting significant pyruvate-kinase flux in this condition. The calculations also show a correlating increase in flux through pyruvate carboxylase (30% with phenylephrine, 15% with glucagon, compared with approximately 50% increases in gluconeogenic flux). The mechanism of this increase is discussed.
为了确定激素诱导的2-氧代戊二酸水平降低是否能通过控制天冬氨酸的生成来调节肝脏从乳酸生成葡萄糖的过程，我们建立了大鼠肝脏线粒体原位生成天冬氨酸的动力学表达式。本实验室先前的研究表明，2-氧代戊二酸可抑制分离的线粒体产生天冬氨酸。本研究旨在探讨在给分离灌注的大鼠肝脏注射可动员Ca2+的生糖激素时观察到的2-氧代戊二酸水平降低的生理意义。首先，对决定分离线粒体中天冬氨酸生成速率的动力学常数进行了估算。然后测量了灌注肝脏中该过程底物和产物的浓度。根据这些值，可以估算线粒体原位的天冬氨酸流出量。当向灌注肝脏中添加胰高血糖素或去氧肾上腺素时，2-氧代戊二酸水平降低，计算出的天冬氨酸生成速率增加。胰高血糖素还对丙酮酸激酶有抑制作用，这一点可由计算出的天冬氨酸流出速率等于糖异生速率这一事实得到证明（两者之差相当于丙酮酸激酶通量）。相比之下，在对照肝脏和去氧肾上腺素刺激下，天冬氨酸的生成高于糖异生，表明在这种情况下存在显著的丙酮酸激酶通量。计算结果还显示，丙酮酸羧化酶的通量相应增加（去氧肾上腺素刺激下增加30%，胰高血糖素刺激下增加15%，而糖异生通量增加约50%）。本文讨论了这种增加的机制。
