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Abstract:
The adhesion molecule on glia, AMOG, an integral cell surface glycoprotein highly expressed by cerebellar astrocytes and involved in neuron to astrocyte adhesion and granule neuron migration (Antonicek, H., Persohn, E., and Schachner, M. (1987) J. Cell Biol. 104, 1587-1595) has been identified as a beta2 subunit isoform of the mouse sodium pump (Gloor, S., Antonicek, H., Sweadner, K.J., Pagliusi, S., Frank, R., Moos, M., and Schachner, M. (1990) J. Cell Biol. 110, 165-174). Here we demonstrate that AMOG/beta2 expressed by cRNA injection in Xenopus oocytes is capable of combining with endogenous Xenopus alpha1 subunits or coexpressed Torpedo alpha1 subunits to yield a functional alpha1/AMOG sodium pump isozyme. Determinations of the number of ouabain binding sites and ouabain-sensitive 86Rb+ uptake suggest that the alpha1/AMOG isozyme has slightly lower maximum transport rate and apparent affinity for external K+ than the alpha1/beta1 isozyme. Immunoprecipitation of alpha1/AMOG complexes from digitonin extracts of [35S]methionine-labeled oocytes with a monoclonal anti-AMOG antibody provides direct evidence for a stable association between AMOG and the alpha1 subunits of Xenopus and Torpedo.
