Chemical and Immunological Characterization of the Two α-N-Acetylgalactosaminidases from Squid Liver

抄録

Based on the inherent α-galactosidase activity, squid liver contains two different α-N-acetylgalactosaminidases (α-GalNAcases): α-N-acetylgalactosaminidase I (α-GalNAcase I), which typically exhibits the α-galactosidase activity and α-N-acetylgalactosaminidase II (α-GalNAcase II), which is devoid of such activity. The molecular properties of the α-GalNAcases that may account for their enzymological differences are as yet unknown. In this study, we have characterized and compared the chemical and immunological properties of α-GalNAcase I and α-GalNAcase II. Analysis of the N-terminal sequence of the first twenty amino acids revealed the striking homology between α-GalNAcase I and α-GalNAcase II. Digestion of α-GalNAcase I and α-GalNAcase II generated the peptide maps that display similarities in peptide pattern, indicating their close relationship in structure. Polyclonal antibodies were generated in rabbits against the purified α-GalNAcase I and α-GalNAcase II for comparison of the immunological properties. Both Western blot and surface plasmon resonance (SPR) studies showed that the anti-α-GalNAcase II antibody reacted with both α-GalNAcase I and α-GalNAcase II, whereas the anti-α-GalNAcase I antibody reacted only with α-GalNAcase I, indicating the presence of common as well as unique antigenic determinants on α-GalNAcase I and α-GalNAcase II. Taken together, these results suggest that α-GalNAcase I and α-GalNAcase II are closely related with regard to structure and that their nonhomologous domains are possibly responsible for the differences in enzymatic properties.