title: Calcium-binding and structural stability of echidna and canine milk lysozymes.
abstract: 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.
authors.affiliation: Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kikuchi
authors.forename: K
authors.initials: K
authors.lastname: Kawano
authors.forename: K
authors.initials: K
authors.lastname: Nitta
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002118:Calcium / Q000737:chemistry; D002942:Circular Dichroism; D004285:Dogs; D004795:Enzyme Stability; D019791:Guanidine / Q000494:pharmacology; D007768:Lactalbumin / Q000737:chemistry; D008892:Milk / Q000201:enzymology*; D008894:Milk Proteins / Q000737:chemistry*; D009113:Muramidase / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D004442:Tachyglossidae
chemical_list: D008894:Milk Proteins; D007768:Lactalbumin; D009113:Muramidase; D019791:Guanidine; D002118:Calcium