Laboratory of Developmental Nutrition, Department of Animal Science, North Carolina State University, Raleigh, NC 27695, USA.
Am J Physiol Regul Integr Comp Physiol. 2010 May;298(5):R1435-43. doi: 10.1152/ajpregu.00634.2009. Epub 2010 Mar 17.
To examine the regulation of hepatic acetogenesis in neonatal swine, carnitine palmitoyltransferase I (CPT I) activity was measured in the presence of varying palmitoyl-CoA (substrate) and malonyl-CoA (inhibitor) concentrations, and [1-(14)C]-palmitate oxidation was simultaneously measured. Accumulation rates of (14)C-labeled acetate, ketone bodies, and citric acid cycle intermediates within the acid-soluble products were determined using radio-HPLC. Measurements were conducted in mitochondria isolated from newborn, 24-h (fed or fasted), and 5-mo-old pigs. Acetate rather than ketone bodies was the predominant radiolabeled product, and its production increased twofold with increasing fatty acid oxidation during the first 24-h suckling period. The rate of acetogenesis was directly proportional to CPT I activity. The high activity of CPT I in 24-h-suckling piglets was not attributable to an increase in CPT I gene expression, but rather to a large decrease in the sensitivity of CPT I to malonyl-CoA inhibition, which offset a developmental decrease in affinity of CPT I for palmitoyl-CoA. Specifically, the IC(50) for malonyl-CoA inhibition and K(m) value for palmitoyl-CoA measured in 24-h-suckling pigs were 1.8- and 2.7-fold higher than measured in newborn pigs. The addition of anaplerotic carbon from malate (10 mM) significantly reduced (14)C accumulation in acetate (P < 0.003); moreover, the reduction was much greater in newborn (80%) than in 24-h-fed (72%) and 5-mo-old pigs (55%). The results demonstrate that acetate is the primary product of hepatic mitochondrial beta-oxidation in Sus scrofa and that regulation during early development is mediated primarily via kinetic modulation of CPT I.
为了研究新生猪肝脏乙醛酸生成的调控，我们在不同的棕榈酰辅酶 A（底物）和丙二酰辅酶 A（抑制剂）浓度下测定肉毒碱棕榈酰转移酶 I（CPT I）的活性，同时测定 [1-(14)C]-棕榈酸的氧化。使用放射性 HPLC 测定酸溶性产物中（14）C 标记的乙酸盐、酮体和柠檬酸循环中间产物的积累速率。测量是在从新生、24 小时（喂养或禁食）和 5 个月大的猪分离的线粒体中进行的。乙酸盐而不是酮体是主要的放射性标记产物，其产量在最初的 24 小时哺乳期间随着脂肪酸氧化的增加而增加两倍。乙醛酸生成的速率与 CPT I 活性直接成正比。24 小时哺乳仔猪中 CPT I 的高活性不是由于 CPT I 基因表达的增加，而是由于 CPT I 对丙二酰辅酶 A 抑制的敏感性大大降低，从而抵消了 CPT I 对棕榈酰辅酶 A 亲和力的发育性下降。具体来说，在 24 小时哺乳仔猪中测量的丙二酰辅酶 A 抑制的 IC（50）和棕榈酰辅酶 A 的 K（m）值分别比新生仔猪高 1.8 倍和 2.7 倍。从苹果酸添加补料碳（10 mM）显著减少了乙酸盐中（14）C 的积累（P < 0.003）；此外，在新生仔猪（80%）中减少的幅度比 24 小时喂养（72%）和 5 个月大的仔猪（55%）中减少的幅度更大。结果表明，乙酸盐是 Sus scrofa 肝脏线粒体β-氧化的主要产物，早期发育期间的调控主要通过 CPT I 的动力学调节来介导。
