Dolenga M, Hechtman P
Centre for Human Genetics, Department of Biology, McGill University, Montreal, Quebec, Canada.
Pediatr Res. 1992 Oct;32(4):479-82. doi: 10.1203/00006450-199210000-00020.
Prolidase deficiency is a rare autosomal recessive disorder characterized by iminodipeptiduria, severe skin ulcers, recurrent infections, and mental retardation. The enzyme prolidase hydrolyzes dipeptides containing C-terminal proline or hydroxyproline. We investigated the metabolic abnormality caused by prolidase deficiency in human cultured skin fibroblasts. These studies were undertaken to test biochemical hypotheses regarding the metabolic origins of the skin lesion occurring in this disease. Our results indicate that prolidase plays a major role in the recycling of dipeptide-bound proline. Control fibroblasts were able to use iminodipeptides in lieu of proline to sustain normal growth, whereas cells homozygous for the prolidase deficiency mutation were not. Proline derived from iminodipeptides diluted incorporation of radiolabeled extracellular proline into cellular protein in normal cells but not in mutant cells. Substitution of a prolidase-free medium for FCS did not affect the growth rate of control cell lines but increased the doubling time of prolidase-deficient cells by 19% (28% in the presence of iminodipeptides). Iminodipeptides added to control and mutant cells maintained in serum-free medium showed no adverse effects on protein synthesis. These results are consistent with a mechanism of biochemical pathology in which proline deprivation caused by the enzyme deficit is a primary cause of damage to skin cells. Prolidase regulation by product and substrate was studied. A 44% decrease in activity was observed in fibroblasts grown for 3 wk in proline-containing medium relative to proline-free medium. However, cells grown in medium in which iminodipeptides replaced proline showed no significant difference in prolidase activity.
脯氨肽酶缺乏症是一种罕见的常染色体隐性疾病，其特征为亚氨基二肽尿症、严重皮肤溃疡、反复感染和智力发育迟缓。脯氨肽酶可水解含有C末端脯氨酸或羟脯氨酸的二肽。我们研究了人类培养的皮肤成纤维细胞中脯氨肽酶缺乏引起的代谢异常。进行这些研究是为了检验关于该疾病中皮肤病变代谢起源的生化假说。我们的结果表明，脯氨肽酶在二肽结合脯氨酸的循环利用中起主要作用。对照成纤维细胞能够使用亚氨基二肽替代脯氨酸来维持正常生长，而脯氨肽酶缺乏突变纯合的细胞则不能。正常细胞中，来自亚氨基二肽的脯氨酸会稀释放射性标记的细胞外脯氨酸掺入细胞蛋白的量，而突变细胞中则不会。用不含脯氨肽酶的培养基替代胎牛血清（FCS）并不影响对照细胞系的生长速率，但使脯氨肽酶缺乏细胞的倍增时间增加了19%（在存在亚氨基二肽的情况下增加了28%）。添加到无血清培养基中培养的对照细胞和突变细胞中的亚氨基二肽对蛋白质合成没有不良影响。这些结果与一种生化病理机制一致，即酶缺乏导致的脯氨酸缺乏是皮肤细胞损伤的主要原因。我们研究了产物和底物对脯氨肽酶的调节作用。与不含脯氨酸的培养基相比，在含脯氨酸的培养基中培养3周的成纤维细胞中，酶活性降低了44%。然而，在亚氨基二肽替代脯氨酸的培养基中培养的细胞，其脯氨肽酶活性没有显著差异。
