Aftring R P, Block K P, Buse M G
Am J Physiol. 1986 May;250(5 Pt 1):E599-604. doi: 10.1152/ajpendo.1986.250.5.E599.
The response of rat skeletal muscle branched-chain alpha-keto acid dehydrogenase to administration of branched-chain amino acids in vivo was determined using a soluble preparation of the enzyme. After detergent extraction of the complex in the presence of kinase and phosphatase inhibitors, initial in vivo activity was typically 1 nmol X min-1 X g muscle-1, with 0.1 mM alpha-[1-14C]ketoisocaproate as substrate. Total activity of the dephosphorylated complex, measured after preincubation with 15 mM Mg2+, typically reached a maximum of 29 nmol X min-1 X g-1. Thus in overnight-fasted rats the complex was 2-3% active. Initial activity increased three- to fivefold after leucine or isoleucine (at higher concentrations) but not valine administration in vivo. After intravenous leucine injection (0.25 mmol/kg) initial muscle enzyme activity increased rapidly and subsequently decreased, paralleling plasma leucine concentrations, while plasma valine and isoleucine decreased. In conclusion, muscle branched-chain alpha-keto acid dehydrogenase complex is rapidly activated when circulating leucine is increased to concentrations that may occur after meals. During hyperleucinemia accelerated valine and isoleucine degradation by muscle may account for the observed "antagonism" among the branched-chain amino acids.
利用该酶的可溶性制剂，测定了大鼠骨骼肌支链α-酮酸脱氢酶在体内对支链氨基酸给药的反应。在激酶和磷酸酶抑制剂存在的情况下，用去污剂提取复合物后，以0.1 mMα-[1-14C]酮异己酸为底物时，体内初始活性通常为1 nmol·min-1·g肌肉-1。用15 mM Mg2+预孵育后测得的去磷酸化复合物的总活性，通常最高可达29 nmol·min-1·g-1。因此，在禁食过夜的大鼠中，该复合物的活性为2%-3%。在体内给予亮氨酸或异亮氨酸（较高浓度）而非缬氨酸后，初始活性增加了三到五倍。静脉注射亮氨酸（0.25 mmol/kg）后，肌肉酶的初始活性迅速增加，随后下降，与血浆亮氨酸浓度平行，而血浆缬氨酸和异亮氨酸浓度下降。总之，当循环亮氨酸增加到餐后可能出现的浓度时，肌肉支链α-酮酸脱氢酶复合物会迅速被激活。在高亮氨酸血症期间，肌肉加速缬氨酸和异亮氨酸的降解可能是观察到的支链氨基酸之间“拮抗作用”的原因。
