Kaneda M, Yonezawa H, Uchikoba T
Department of Chemistry, Faculty of Science, Kagoshima University, Japan.
Biotechnol Appl Biochem. 1995 Oct;22(2):215-22.
Cucumisin (EC 3.4.21.25), a serine endopeptidase, was isolated by a simple purification procedure from the prince melon (Cucumis melo ssp. melo, cv. 'Prince Melon'). The enzyme is stable over a wide pH range (4-11) and to heat, 80% of its initial activity remaining even at pH 11.1 and at 60 degrees C for 20 min. The enzyme was inactive at 72 degrees C and pH 8.0, but 38% of the activity remained in the presence of 10% (w/v) glycerol. Caseinolysis by cucumisin indicated full activity in 8 M urea at pH 9.1 and 50 degrees C. Cucumisin was inactivated by treatment with trypsin at 37 degrees C for 24 h, but was not affected by alpha-chymotrypsin. The synthetic substrates benzyloxycarbonyltyrosine nitrophenyl ester (Z-Tyr-ONp) and benzoyltyrosine ethyl ester (Bz-Tyr-OEt) were cleaved, but Z-Lys-ONp and tosylarginine methyl ester (Tos-Arg-OMe) were not cleaved by cucumisin. Oxidized insulin B-chain was hydrolysed by cucumisin at 37 degrees C for 24 h, 21 cleavage sites being detected. Cucumisin could not cleave the C-termini of all the valine residues in the oxidized insulin B-chain molecule.
黄瓜蛋白酶（EC 3.4.21.25）是一种丝氨酸内肽酶，通过简单的纯化程序从王子甜瓜（甜瓜变种甜瓜，品种‘王子甜瓜’）中分离得到。该酶在较宽的pH范围（4 - 11）内稳定，且耐热，即使在pH 11.1和60℃下处理20分钟，仍保留80%的初始活性。该酶在72℃和pH 8.0时无活性，但在10%（w/v）甘油存在下仍保留38%的活性。黄瓜蛋白酶在pH 9.1和50℃的8 M尿素中对酪蛋白的水解显示出完全活性。黄瓜蛋白酶在37℃下用胰蛋白酶处理24小时会失活，但不受α-胰凝乳蛋白酶影响。合成底物苄氧羰基酪氨酸硝基苯酯（Z-Tyr-ONp）和苯甲酰酪氨酸乙酯（Bz-Tyr-OEt）可被切割，但Z-赖氨酸硝基苯酯（Z-Lys-ONp）和甲苯磺酰精氨酸甲酯（Tos-Arg-OMe）不能被黄瓜蛋白酶切割。氧化胰岛素B链在37℃下经黄瓜蛋白酶水解24小时，检测到21个切割位点。黄瓜蛋白酶不能切割氧化胰岛素B链分子中所有缬氨酸残基的C末端。
