Gaspar L, Chan J S, Seidah N G, Chrétien M
J Clin Endocrinol Metab. 1984 Oct;59(4):614-21. doi: 10.1210/jcem-59-4-614.
The NH2-terminal fragment (hNT) of proopiomelanocortin is found predominantly as one molecular form of apparent mol wt of 12K in the circulation. Since the kidney may play an important role in the elimination and degradation of proopiomelanocortin-related peptides, we analyzed the urinary forms of immunoreactive hNT (IR-hNT) by molecular sieving and carbohydrate affinity (Concanavalin A-agarose) chromatography. RIA specific for the amino terminal portion and for the gamma 3-MSH (carboxy-terminal portion of hNT) were used in these studies. Molecular sieve chromatography revealed several forms of IR-hNT in the urine from normal subjects, patients with Nelson's syndrome, and patients with ectopic ACTH-secreting tumors. A considerable decrease in IR-hNT and IR-gamma 3-MSH was found in the urine of a patient with ACTH deficiency and normal subjects during glucocorticoid suppression. In urine from normal subjects and a patient with lung cancer not causing Cushing's syndrome, the majority of amino-terminal IR-hNT (66-83%) had apparent mol wts of 3-4K, 6-7K, and 8-10K, and did not cross-react with the gamma 3-MSH antiserum. Ten to nineteen percent of the total IR-hNT was eluted in the position of authentic hNT and reacted with the gamma 3-MSH RIA. In patients with Nelson's syndrome and those with ectopic ACTH syndrome, almost no intact hNT (less than 7% of the total) was present in urine; most of the IR-hNT appeared in the elution volumes with an apparent mol wt of 8-10K. In addition, smaller forms (6-7K and 3-4K) of hNT were also detected in the urine of these patients. The major form of urinary IR-gamma 3-MSH exhibited an apparent mol wt of 7-8K and did not correspond to any of the peaks of IR-hNT. Carbohydrate affinity chromatography (Concanavalin A-agarose) of smaller forms of IR-hNT revealed weak affinity to the lectin, which suggests loss of the carbohydrate moiety during renal excretion. We conclude that hNT in urine is present in extensively cleaved forms and that deglycosylation may be an important step in hNT degradation. These results support a role for the kidney in the catabolism of hNT.
阿黑皮素原的氨基末端片段（hNT）在循环中主要以一种表观分子量为12K的分子形式存在。由于肾脏可能在阿黑皮素原相关肽的清除和降解中起重要作用，我们通过分子筛和碳水化合物亲和（伴刀豆球蛋白A - 琼脂糖）色谱分析了免疫反应性hNT（IR - hNT）的尿中形式。在这些研究中使用了对氨基末端部分和γ3 - MSH（hNT的羧基末端部分）具有特异性的放射免疫分析。分子筛色谱显示正常受试者、尼尔森综合征患者和异位促肾上腺皮质激素分泌肿瘤患者的尿液中有几种IR - hNT形式。在糖皮质激素抑制期间，促肾上腺皮质激素缺乏患者和正常受试者的尿液中IR - hNT和IR - γ3 - MSH显著减少。在正常受试者和未引起库欣综合征的肺癌患者的尿液中，大多数氨基末端IR - hNT（66 - 83%）的表观分子量为3 - 4K、6 - 7K和8 - 10K，并且不与γ3 - MSH抗血清发生交叉反应。总IR - hNT的10%至19%在 authentic hNT的位置洗脱，并与γ3 - MSH放射免疫分析发生反应。在尼尔森综合征患者和异位促肾上腺皮质激素综合征患者的尿液中，几乎不存在完整的hNT（占总量的不到7%）；大多数IR - hNT出现在表观分子量为8 - 10K的洗脱体积中。此外，在这些患者的尿液中也检测到了较小形式（6 - 7K和3 - 4K）的hNT。尿中IR - γ3 - MSH的主要形式表现出表观分子量为7 - 8K，并且与IR - hNT的任何峰均不对应。较小形式的IR - hNT的碳水化合物亲和色谱（伴刀豆球蛋白A - 琼脂糖）显示对凝集素的亲和力较弱，这表明在肾脏排泄过程中碳水化合物部分丢失。我们得出结论，尿中的hNT以广泛裂解的形式存在并且去糖基化可能是hNT降解的重要步骤。这些结果支持肾脏在hNT分解代谢中的作用。
