Kikuchi M, Kawano K, Nitta K
Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
Protein Sci. 1998 Oct;7(10):2150-5. doi: 10.1002/pro.5560071012.
For echidna and canine milk lysozymes, which were presumed to be the calcium-binding lysozymes by their amino acid sequences, we have quantitated their calcium-binding strength and examined their guanidine unfolding profiles. The calcium-binding constants of echidna and canine lysozymes were determined to be 8.6 x 10(6) M(-1) and 8.9 x 10(6) M(-1) in 0.1 M KCl at pH 7.1 and 20 C, respectively. The unfolding of decalcified canine lysozyme proceeds in the same manner as that of alpha-lactalbumin, through a stable molten globule intermediate. However, neither calcium-bound nor decalcified echidna lysozyme shows a stable molten globule intermediate. This unfolding profile of echidna lysozyme is identical to that of conventional lysozymes and pigeon egg-white lysozyme, avian calcium-binding lysozyme. This result supports the suggestion of Prager and Jolles (Prager EM, Jolles P. 1996. Animal lysozymes c and g: An overview. In: Jolles P, ed. Lysozymes: Model enzymes in biochemistry and biology. Basel-Boston-Berlin: Birkhauzer Verlag. pp 9-31) that the lineage of avian and echidna calcium-binding lysozymes and that of eutherian calcium-binding lysozymes diverged separately from that of conventional lysozymes.
对于针鼹和犬类的乳溶菌酶，根据其氨基酸序列推测它们为钙结合溶菌酶，我们已对其钙结合强度进行了定量，并研究了它们的胍变性曲线。在pH 7.1、20℃的0.1 M KCl中，针鼹和犬类溶菌酶的钙结合常数分别测定为8.6×10⁶ M⁻¹和8.9×10⁶ M⁻¹。脱钙犬类溶菌酶的变性过程与α-乳白蛋白相同，通过一个稳定的熔球中间体进行。然而，无论是结合钙的还是脱钙的针鼹溶菌酶都未显示出稳定的熔球中间体。针鼹溶菌酶的这种变性曲线与传统溶菌酶以及鸽蛋清溶菌酶（鸟类钙结合溶菌酶）的相同。这一结果支持了普拉格和乔勒斯（普拉格EM，乔勒斯P。1996。动物溶菌酶c和g：概述。见：乔勒斯P编。溶菌酶：生物化学和生物学中的模型酶。巴塞尔 - 波士顿 - 柏林：伯克霍夫出版社。第9 - 31页）的观点，即鸟类和针鼹钙结合溶菌酶的谱系以及真兽类钙结合溶菌酶的谱系与传统溶菌酶的谱系是分别分化的。
