绵羊肝脏中由丙酸合成磷酸烯醇丙酮酸

Synthesis of phosphoenolpyruvate from propionate in sheep liver.

作者信息

Smith R M, Osborne-White W S

出版信息

Biochem J. 1971 Oct;124(5):867-76. doi: 10.1042/bj1240867.

DOI:10.1042/bj1240867

PMID:4331860

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC1177273/

Abstract

Utilization of propionate by sheep liver mitochondria was stimulated equally by pyruvate or alpha-oxoglutarate, with formation predominantly of malate. Pyruvate increased conversion of propionate carbon into citrate, whereas alpha-oxoglutarate increased formation of phosphoenolpyruvate. The fraction of metabolized propionate converted into phosphoenolpyruvate was about 17% in the presence or absence of alpha-oxoglutarate and about 7% in the presence of pyruvate. Pyruvate consumption was inhibited by 80% by 5mm-propionate. 2. Compared with rat liver, sheep liver was characterized by very high activities of phosphoenolpyruvate carboxykinase and moderately high activities of aconitase in the mitochondria and by low activities of ;malic' enzyme, pyruvate kinase and lactate dehydrogenase in the cytosol. Activities of phosphoenolpyruvate carboxy-kinase were similar in liver cytosol from rats and sheep. Activities of malate dehydrogenase and NADP-linked isocitrate dehydrogenase in sheep liver were about half those in rat liver. 3. The phosphate-dicarboxylate antiport was active in sheep liver mitochondria, but compared with rat liver mitochondria the citrate-malate antiport showed only low activity and mitochondrial aconitase was relatively inaccessible to external citrate. The rate of swelling of mitochondria induced by phosphate in solutions of ammonium malate was inversely related to the concentration of malate. 4. The results are discussed in relation to gluconeogenesis from propionate in sheep liver. It is proposed that propionate is converted into malate by the mitochondria and the malate is converted into phosphoenolpyruvate by enzymes in the cytosol. In this way sufficient NADH would be generated in the cytosol to convert the phosphoenolpyruvate into glucose.

摘要

绵羊肝线粒体对丙酸盐的利用受到丙酮酸或α-酮戊二酸的同等刺激，主要生成苹果酸。丙酮酸增加了丙酸盐碳向柠檬酸的转化，而α-酮戊二酸增加了磷酸烯醇丙酮酸的生成。在有或没有α-酮戊二酸存在的情况下，代谢的丙酸盐转化为磷酸烯醇丙酮酸的比例约为17%，在有丙酮酸存在的情况下约为7%。5mmol/L的丙酸盐可抑制丙酮酸消耗80%。2. 与大鼠肝脏相比，绵羊肝脏的特点是线粒体中磷酸烯醇丙酮酸羧激酶活性非常高，乌头酸酶活性中等偏高，而胞质溶胶中“苹果酸”酶、丙酮酸激酶和乳酸脱氢酶活性较低。大鼠和绵羊肝脏胞质溶胶中磷酸烯醇丙酮酸羧激酶的活性相似。绵羊肝脏中苹果酸脱氢酶和NADP连接的异柠檬酸脱氢酶的活性约为大鼠肝脏的一半。3. 磷酸-二羧酸反向转运体在绵羊肝线粒体中具有活性，但与大鼠肝线粒体相比，柠檬酸-苹果酸反向转运体活性较低，线粒体乌头酸酶相对不易接触到外部柠檬酸。苹果酸铵溶液中磷酸盐诱导的线粒体肿胀速率与苹果酸浓度呈负相关。4. 结合绵羊肝脏中丙酸盐的糖异生作用对结果进行了讨论。提出丙酸盐先由线粒体转化为苹果酸，然后苹果酸再由胞质溶胶中的酶转化为磷酸烯醇丙酮酸。通过这种方式，胞质溶胶中会产生足够的NADH，将磷酸烯醇丙酮酸转化为葡萄糖。