Centro de Investigaciones Biológicas del Noroeste-CIBNOR, Mar Bermejo 195, Col. Playa Palo de Santa Rita, La Paz, B.C.S. 23096, Mexico.
Mar Biotechnol (NY). 2013 Feb;15(1):87-96. doi: 10.1007/s10126-012-9461-4. Epub 2012 May 31.
Aspartic proteinases in the gastric fluid of clawed lobsters Homarus americanus and Homarus gammarus were isolated to homogeneity by single-step pepstatin-A affinity chromatography; such enzymes have been previously identified as cathepsin D-like enzymes based on their deduced amino acid sequence. Here, we describe their biochemical characteristics; the properties of the lobster enzymes were compared with those of its homolog, bovine cathepsin D, and found to be unique in a number of ways. The lobster enzymes demonstrated hydrolytic activity against synthetic and natural substrates at a wider range of pH; they were more temperature-sensitive, showed no changes in the K(M) value at 4°C, 10°C, and 25°C, and had 20-fold higher k(cat)/K(M) values than bovine enzyme. The bovine enzyme was temperature-dependent. We propose that both properties arose from an increase in molecular flexibility required to compensate for the reduction of reaction rates at low habitat temperatures. This is supported by the fast denaturation rates induced by temperature.
爪龙虾美洲螯龙虾和罗氏沼虾的胃液中的天冬氨酸蛋白酶通过一步法胃蛋白酶 A 亲和层析被分离到均一性；这些酶以前根据它们的推导氨基酸序列被鉴定为组织蛋白酶 D 样酶。在这里，我们描述了它们的生化特性；龙虾酶的性质与同源物牛组织蛋白酶 D 的性质进行了比较，发现它们在许多方面具有独特性。龙虾酶在更宽的 pH 范围内对合成和天然底物表现出水解活性；它们对温度更敏感，在 4°C、10°C 和 25°C 时 K(M)值没有变化，k(cat)/K(M)值比牛酶高 20 倍。牛酶是温度依赖性的。我们提出，这两种特性都源于分子灵活性的增加，这是为了补偿在低栖息地温度下反应速率的降低。这一假设得到了由温度引起的快速变性速率的支持。
