Herzberg G R, Brosnan J T, Hall B, Rogerson M
Department of Biochemistry, Memorial University of Newfoundland, St. Johns, Canada.
Am J Physiol. 1988 Jun;254(6 Pt 2):R903-7. doi: 10.1152/ajpregu.1988.254.6.R903.
Phosphoenolpyruvate carboxykinase (PEPCK) in murre liver occurs in both cytoplasmic and mitochondrial forms. During a 3-day fast, hepatic PEPCK increases from 9.1 U/g with 19% cytosolic to 12.2 U/g with 35% cytosolic. The increase in activity is due almost entirely to increased cytosolic activity. PEPCK in murre kidney was present only in the mitochondrial compartment. Gluconeogenesis in vitro was determined in both hepatocytes and kidney tubules isolated from 3-day-fasted murres. In hepatocytes, lactate was the best substrate, but both pyruvate and alanine were good gluconeogenic substrates. This observation is consistent with the existence of a cytosolic form of PEPCK. In the kidney, glycerol was the best substrate but was only slightly better than lactate. Alanine and pyruvate were not as effective as gluconeogenic precursors, presumably because of the lack of cytosolic PEPCK. We propose that the major site of gluconeogenesis from amino acids in the murre is the liver, since this is a much larger organ than the kidney and has a cytosolic form of PEPCK necessary for gluconeogenesis from oxidized substrates.
斑海雀肝脏中的磷酸烯醇式丙酮酸羧激酶（PEPCK）存在于细胞质和线粒体两种形式中。在为期3天的禁食期间，肝脏中的PEPCK从9.1 U/g（细胞质形式占19%）增加到12.2 U/g（细胞质形式占35%）。活性的增加几乎完全归因于细胞质活性的增加。斑海雀肾脏中的PEPCK仅存在于线粒体部分。从禁食3天的斑海雀中分离出的肝细胞和肾小管中均测定了体外糖异生情况。在肝细胞中，乳酸是最佳底物，但丙酮酸和丙氨酸都是良好的糖异生前体。这一观察结果与细胞质形式的PEPCK的存在一致。在肾脏中，甘油是最佳底物，但仅略优于乳酸。丙氨酸和丙酮酸作为糖异生前体的效果不佳，推测是由于缺乏细胞质PEPCK。我们认为，斑海雀中氨基酸糖异生的主要部位是肝脏，因为肝脏比肾脏大得多，且具有从氧化底物进行糖异生所需的细胞质形式的PEPCK。
