Schadewaldt P, Wendel U
Institut für Physiologische Chemie II, Universität Düsseldorf, FRG.
Pediatr Res. 1987 Nov;22(5):591-4. doi: 10.1203/00006450-198711000-00022.
Using 1-14C-labeled substrates, the metabolism of naturally occurring branched-chain L-amino acids was studied in incubations with cultured human skin fibroblasts derived from normal subjects and from a patient with maple syrup urine disease (variant form). Practically saturating conditions were reached at 1 mmol/liter of substrate and metabolic rates remained essentially constant up to 120 min. In control fibroblasts, the transamination of 14C-labeled leucine, valine, isoleucine, and allo-isoleucine (1 mmol/liter) was about 26, 13, 12, and 5 nmol/90 min/mg of cell protein, respectively. The portion of transamination products undergoing oxidative decarboxylation within the cells was about 17, 43, 34, and 23%, respectively. With the maple syrup urine disease cell line, comparable transamination rates were found. As compared to the findings with normal cells, however, 14CO2 production from the above mentioned substrates was reduced and amounted to 14, 11, 25, and 45%, respectively. Thus it appeared that residual branched-chain 2-oxo acid dehydrogenase activity was differently reduced towards the four 2-oxo acid substrates.
利用1-¹⁴C标记的底物，在与来自正常受试者和枫糖尿症患者（变异型）的培养人皮肤成纤维细胞一起孵育的过程中，研究了天然存在的支链L-氨基酸的代谢情况。在底物浓度为1 mmol/升时达到了几乎饱和的条件，并且代谢率在长达120分钟内基本保持恒定。在对照成纤维细胞中，¹⁴C标记的亮氨酸、缬氨酸、异亮氨酸和别异亮氨酸（1 mmol/升）的转氨作用分别约为26、13、12和5 nmol/90分钟/毫克细胞蛋白。细胞内经历氧化脱羧的转氨产物比例分别约为17%、43%、34%和23%。在枫糖尿症细胞系中，发现了相当的转氨速率。然而，与正常细胞的结果相比，上述底物产生的¹⁴CO₂减少，分别为14%、11%、25%和45%。因此，似乎残余的支链2-氧代酸脱氢酶活性对四种2-氧代酸底物的降低程度不同。
