Yeh Y Y
Arch Biochem Biophys. 1984 Aug 15;233(1):10-8. doi: 10.1016/0003-9861(84)90596-4.
Leucine is catabolized to ketone bodies in adipose tissue, but the contribution of this output to overall ketone metabolism is not known. The intent of the present study was to determine the capacity of different adipose tissues to synthesize ketone bodies from leucine. The amino acid was readily converted into acetoacetate in epididymal, perirenal, and omental fat tissues. In rats fed ad libitum, the rate of acetoacetate synthesis in omental fat (about 2 mumol g tissue-1h-1) was at least 8 times higher than in epididymal or perirenal fat. In omental fat, the rates of acetoacetate formation from alpha-ketoisocaproic acid were 47-55% lower than from leucine at all concentrations examined. There was no significant synthesis of beta-hydroxybutyrate from leucine or alpha-ketoisocaproic acid. After oxidative decarboxylation, a greater proportion (about three-fourths) of leucine in omental fat was metabolized to acetoacetate than to CO2 production through the Krebs cycle. Although addition of glucose, pyruvate, or carnitine did not affect the production of acetoacetate, fasting for 24 h stimulated acetoacetate synthesis from leucine and alpha-ketoisocaproic acid in omental fat. The high rate of leucine conversion to acetoacetate in omental fat was related to high activities of leucine aminotransferase and branched-chain alpha-keto acid dehydrogenase. Moreover, protein content and cytochrome c oxidase activity of omental mitochondria were, respectively, 13 and 12 times higher than in epididymal mitochondria. In contrast, fat content of epididymal adipose tissue was 21 times that of omental adipose tissue. Epididymal depot consisted of 2.0% protein and 75.8% fat, whereas omental depot contains 17.2% protein and 3.6% fat, resembling that of liver and muscle. The results suggest that the high ketogenic capacity of omental fat stems in part from an augmented mitochondrial mass and high activity of branched-chain alpha-keto acid dehydrogenase.
亮氨酸在脂肪组织中分解代谢生成酮体，但这种产出对整体酮代谢的贡献尚不清楚。本研究的目的是确定不同脂肪组织从亮氨酸合成酮体的能力。在附睾、肾周和网膜脂肪组织中，该氨基酸很容易转化为乙酰乙酸。在自由采食的大鼠中，网膜脂肪中乙酰乙酸的合成速率（约2 μmol g组织-1h-1）至少比附睾或肾周脂肪高8倍。在网膜脂肪中，在所有检测浓度下，由α-酮异己酸生成乙酰乙酸的速率比由亮氨酸生成的速率低47 - 55%。亮氨酸或α-酮异己酸均未显著合成β-羟基丁酸。氧化脱羧后，网膜脂肪中亮氨酸经代谢生成乙酰乙酸的比例（约四分之三）大于通过三羧酸循环生成二氧化碳的比例。虽然添加葡萄糖、丙酮酸或肉碱不影响乙酰乙酸的生成，但禁食24小时可刺激网膜脂肪中亮氨酸和α-酮异己酸生成乙酰乙酸。网膜脂肪中亮氨酸转化为乙酰乙酸的高速率与亮氨酸转氨酶和支链α-酮酸脱氢酶的高活性有关。此外，网膜线粒体的蛋白质含量和细胞色素c氧化酶活性分别比附睾线粒体高13倍和12倍。相比之下，附睾脂肪组织的脂肪含量是网膜脂肪组织的21倍。附睾脂肪库由2.0%的蛋白质和75.8%的脂肪组成，而网膜脂肪库含有17.2%的蛋白质和3.6%的脂肪，类似于肝脏和肌肉。结果表明，网膜脂肪的高生酮能力部分源于线粒体数量的增加和支链α-酮酸脱氢酶的高活性。
