ABSTRACT
Based on the inherent alpha-galactosidase activity, squid liver contains two different alpha-N-acetylgalactosaminidases (alpha-GalNAcases): alpha-N-acetylgalactosaminidase I (alpha-GalNAcase I), which typically exhibits the alpha-galactosidase activity and alpha-N-acetylgalactosaminidase II (alpha-GalNAcase II), which is devoid of such activity. The molecular properties of the alpha-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 alpha-GalNAcase I and alpha-GalNAcase II. Analysis of the N-terminal sequence of the first twenty amino acids revealed the striking homology between alpha-GalNAcase I and alpha-GalNAcase II. Digestion of alpha-GalNAcase I and alpha-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 alpha-GalNAcase I and alpha-GalNAcase II for comparison of the immunological properties. Both Western blot and surface plasmon resonance (SPR) studies showed that the anti-alpha-GalNAcase II antibody reacted with both alpha-GalNAcase I and alpha-GalNAcase II, whereas the anti-alpha-GalNAcase I antibody reacted only with alpha-GalNAcase I, indicating the presence of common as well as unique antigenic determinants on alpha-GalNAcase I and alpha-GalNAcase II. Taken together, these results suggest that alpha-GalNAcase I and alpha-GalNAcase II are closely related with regard to structure and that their nonhomologous domains are possibly responsible for the differences in enzymatic properties.
Subject(s)
Decapodiformes/enzymology , Epitopes/immunology , Liver/enzymology , alpha-N-Acetylgalactosaminidase/chemistry , alpha-N-Acetylgalactosaminidase/immunology , Amino Acid Sequence , Animals , Blotting, Western , Electrophoresis, Polyacrylamide Gel , Epitope Mapping , Isoenzymes , Molecular Sequence Data , Peptide Mapping , Sequence Homology, Amino Acid , Surface Plasmon Resonance , alpha-N-Acetylgalactosaminidase/isolation & purificationABSTRACT
We have previously shown that in Dictyostelium cells a 32 kDa protein is rapidly and completely dephosphorylated in response to starvation that is essential for the initiation of differentiation (Akiyama & Maeda 1992). In the present work, this phosphoprotein was identified as a homologue (Dd-RPS6) of ribosomal protein S6 (RPS6) that is an essential member for protein synthesis. As expected, Dd-RPS6 seems to be absolutely required for cell survival, because we failed to obtain antisense-RNA mediated cells as well as Dd-rps6-null cells by homologous recombination in spite of many trials. In many kinds of cell lines, RPS6 is known to be located in the nucleus and cytosol, but Dd-RPS6 is predominantly located in the cell cortex with cytoskeletons, and in the contractile ring of just-dividing cells. In this connection, the overexpression of Dd-RPS6 greatly impairs cytokinesis during axenic shake-cultures in growth medium, resulting in the formation of multinucleate cells. Much severe impairment of cytokinesis was observed when Dd-RPS6-overexpressing cells (Dd-RPS6(OE) cells) were incubated on a living Escherichia coli lawn. The initiation of differentiation triggered by starvation was also delayed in Dd-RPS6(OE) cells. In addition, Dd-RPS6(OE) cells exhibit defective differentiation into prespore cells and spores during late development. Thus, it is likely that the proper expression of Dd-RPS6 may be of importance for the normal progression of late differentiation as well as for the initiation of differentiation.
