Studies on the cysteine proteinase inhibitor (cystatin S)

从人全唾液中纯化出8种与胱抑素S抗血清反应的蛋白（暂时命名为胱抑素SN、S2、S3、SA、S6、S7和S8）。研究了它们对无花果蛋白、木瓜蛋白酶和二肽基肽酶I的氨基末端序列和Ki值。S4、S6和S8缺少胱抑素S的n端9、7和4个残基，而胱抑素SA和胱抑素S7在其n端分别有4个和3个残基的延伸。它们对无花果素和木瓜蛋白酶均有抑制作用，但Ki值不同。由于胱抑素SN和SA存在氨基酸取代现象，对它们的整体结构进行了序列研究。这些结果表明，与胱抑素S结构密切相关的蛋白及其降解或延长的蛋白构成了唾液中半胱氨酸蛋白酶抑制剂家族。半胱氨酸蛋白酶抑制剂由于氨基酸取代而具有很大的活性差异，被认为用于调节唾液和唾液腺中的蛋白酶活性，并保护口腔组织免受酶的攻击。采用Ouchterlony法研究抗原在人体液（血清、尿液、泪液、全唾液、颌下-舌下唾液、腮腺唾液）中的分布。当标本不加浓度测试时，泪液、全唾液和上颌下-舌下唾液均呈阳性。

Eight proteins which react with anti-cystatin S antiserum were purified to the electrophoretically homogeneous state from human whole saliva (temporarily named cystatin SN, S2, S3, SA, S6, S7 and S8). Their amino terminal sequences and Ki values for ficin,papain and dipeptidyl peptidase I were studied. S4, S6 and S8 lack N-terminal 9, 7 and 4 residues of cystatin S, while cystatin SA and cystatin S7 have extension of 4 and 3 residues at its N-terminus respectively. All of them show inhibitory activity for ficin and papain but have different Ki values. As amino acid substitutions were observed in cased of cystatin SN and SA, sequence study of their whole structures were undertaken. Both of them appered to have 90% sequence homology with cystatin S. These results suggest that cystatin S, proteins with structures related colsely to cystatin S, and their degraded or elongated proteins constitute a family of cysteine proteinase inhibitor in saliva. Cysteine proteinase inhibitors having the wide difference in the activity as the result of amino acid substitutions are considered to serve for the regulation of proteinase activity in saliva and salivary glands and for protection of oral tissues from enzymic attack. The Ouchterlony method was used to study the distribution of the antigen in human body fluids (serum, urine, tear, whole saliva, submaxillary-sublingual saliva, parotid saliva). When specimens were tested without concentration, tear, whole saliva, and submaxillary-sublingual saliva gave the positive results.