Tein I, Demaugre F, Bonnefont J P, Saudubray J M
Clinique et Unité de Recherche de génétique médicale, INSERM U12, Hôpital des Enfants Malades, Paris, France.
J Neurol Sci. 1989 Sep;92(2-3):229-45. doi: 10.1016/0022-510x(89)90139-1.
Human carnitine palmitoyltransferase (CPT) deficiency results in 2 clinical forms: a more common "muscular form" with myoglobinuria with or without delayed or impaired ketogenesis and a rare "hepatic form" with hypoketotic hypoglycemia, encephalopathy and seizures without muscular manifestations. We present 2 patients, a male (patient 1) and a female (patient 2) with infantile "hepatic" CPT deficiency and previously documented CPT1 deficiency in fibroblasts. In patient 2, a deficiency of "total" CPT activity in liver had also been previously documented. We set up an isotope exchange assay system that effectively differentiated CPT1 and CPT2 activities in muscle. We found normal CPT1 and CPT2 activities in our patients under near saturating substrate conditions. The CPT1 and CPT2 activities were suppressed to a strikingly similar degree under different kinetic conditions as compared to control muscle and were found to have similar Km values for carnitine and PCoA. With Km concentrations of carnitine, the mean residual activities of CPT1 for patients 1 and 2 were 49 and 44%, respectively (control range 40-53%); the mean residual activities of CPT2 were 60 and 46%, respectively (control range 49-59%). With Km concentrations of PCoA, the mean residual activities of CPT1 for patients 1 and 2 were 52 and 58%, respectively (control range of 52-59%); mean residual activities of CPT2 were 54% and 56%, respectively (control range of 51-68%). When the Vmax concentration of PCoA was doubled and bovine serum albumin reduced to 0.1%, the mean residual activities of CPT1 for patients 1 and 2 were 69 and 63%, respectively (control range 60-80%). In "muscular" patients, a marked absolute deficiency of CPT2 activity (less than 12% residual) was found with an apparent increased sensitivity to suppression of enzymatic activity when the Km concentration of carnitine was used. We suggest that CPT1 and CPT2 may be separate proteins. Furthermore, CPT1 itself may exist as tissue-specific isoforms being the same protein in liver and fibroblasts and a different protein in muscle. Either could be encoded for by the same or closely related genes.
人类肉碱棕榈酰转移酶（CPT）缺乏症有两种临床形式：一种较常见的“肌肉型”，伴有或不伴有延迟或受损的生酮作用的肌红蛋白尿；另一种罕见的“肝脏型”，伴有低酮性低血糖、脑病和癫痫发作，但无肌肉表现。我们报告了2例患者，1例男性（患者1）和1例女性（患者2），患有婴儿期“肝脏型”CPT缺乏症，且之前已记录成纤维细胞中CPT1缺乏。在患者2中，之前也已记录肝脏中“总”CPT活性缺乏。我们建立了一种同位素交换测定系统，可有效区分肌肉中的CPT1和CPT2活性。我们发现，在接近饱和底物条件下，我们的患者中CPT1和CPT2活性正常。与对照肌肉相比，在不同动力学条件下，CPT1和CPT2活性被抑制的程度惊人地相似，并且发现它们对肉碱和PCoA具有相似的Km值。在肉碱的Km浓度下，患者1和患者2的CPT1平均残余活性分别为49%和44%（对照范围为40 - 53%）；CPT2的平均残余活性分别为60%和46%（对照范围为49 - 59%）。在PCoA的Km浓度下，患者1和患者2的CPT1平均残余活性分别为52%和58%（对照范围为52 - 59%）；CPT2的平均残余活性分别为54%和56%（对照范围为51 - 68%）。当PCoA的Vmax浓度加倍且牛血清白蛋白降至0.1%时，患者1和患者2的CPT1平均残余活性分别为69%和63%（对照范围为60 - 80%）。在“肌肉型”患者中，当使用肉碱的Km浓度时，发现CPT2活性明显绝对缺乏（残余活性小于12%），且酶活性抑制的敏感性明显增加。我们认为CPT1和CPT2可能是不同的蛋白质。此外，CPT1本身可能以组织特异性同工型存在，在肝脏和成纤维细胞中是同一种蛋白质，而在肌肉中是不同的蛋白质。两者可能由相同或密切相关的基因编码。
