Thampy K G, Koshy A G
Fort Wayne Center for Medical Education, IN.
J Lipid Res. 1991 Oct;32(10):1667-73.
Acetyl-CoA carboxylase catalyzes the first committed step in the synthesis of fatty acids. Because fatty acids are required during myelination in the developing brain, it was proposed that the level of acetyl-CoA carboxylase may be highest in embryonic brain. The presence of acetyl-CoA carboxylase activity was detected in chick embryo brain. Its activity varied with age, showing a peak in the 17-18-day-old embryo and decreasing thereafter. The enzyme, affinity-purified from 18-day-old chick embryo brain, appeared as a major protein band on polyacrylamide electrophoresis gels in the presence of sodium dodecyl sulfate (Mr 265,000), indistinguishable from the 265 kDa isozyme of liver acetyl-CoA carboxylase. It had significant activity (Sp act = 1.1 mumol/min per mg protein) in the absence of citrate. There was a maximum stimulation of only 25% in the presence of citrate. Dephosphorylation using [acetyl-CoA carboxylase] phosphatase 2 did not result in activation of the enzyme. Palmitoyl-CoA (0.1 mM) and malonyl-CoA (1 mM) inhibited the activity to 95% and 71%, respectively. Palmitoylcarnitine, however, did not show significant inhibition. The enzyme was inhibited (greater than 95%) by avidin; however, avidin did not show significant inhibition in the presence of excess biotin. The enzyme was also inhibited (greater than 90%) by antibodies against liver acetyl-CoA carboxylase. An immunoblot or avidin-blot detected only one protein band (Mr 265,000) in preparations from chick embryo brain or adult liver. These observations suggest that acetyl-CoA carboxylase is present in embryonic brain and that the enzyme appears to be similar to the 265 kDa isozyme of liver.
乙酰辅酶A羧化酶催化脂肪酸合成的首个关键步骤。由于发育中的大脑在髓鞘形成过程中需要脂肪酸，因此有人提出乙酰辅酶A羧化酶的水平在胚胎大脑中可能最高。在鸡胚脑中检测到了乙酰辅酶A羧化酶活性。其活性随年龄变化，在17 - 18日龄胚胎中达到峰值，此后下降。从18日龄鸡胚脑中亲和纯化得到的该酶，在十二烷基硫酸钠存在下，在聚丙烯酰胺电泳凝胶上呈现为一条主要蛋白带（分子量265,000），与肝脏乙酰辅酶A羧化酶的265 kDa同工酶无法区分。在没有柠檬酸的情况下，它具有显著活性（比活性 = 1.1微摩尔/分钟每毫克蛋白）。在有柠檬酸存在时，最大刺激仅为25%。使用[乙酰辅酶A羧化酶]磷酸酶2进行去磷酸化并未导致该酶激活。棕榈酰辅酶A（0.1毫摩尔）和丙二酰辅酶A（1毫摩尔）分别将活性抑制至95%和71%。然而，棕榈酰肉碱并未表现出显著抑制作用。该酶被抗生物素蛋白抑制（超过95%）；然而，在过量生物素存在下，抗生物素蛋白并未表现出显著抑制作用。该酶也被抗肝脏乙酰辅酶A羧化酶的抗体抑制（超过90%）。免疫印迹或抗生物素蛋白印迹在鸡胚脑或成年肝脏的制剂中仅检测到一条蛋白带（分子量265,000）。这些观察结果表明乙酰辅酶A羧化酶存在于胚胎大脑中，并且该酶似乎与肝脏的265 kDa同工酶相似。
