CHARACTERIZATION OF THE HUMAN Na+, K+-ATPASE ALPHA 4 ISOFORM

by Hlivko, Jonathan Thomas

Four Na+, K+-ATPase alpha isoforms have been identified and characterized in the rat. In humans, three isoforms have been characterized and evidence has been provided suggesting the existence of a fourth alpha isoform. The goal of this study was to isolate and characterize the fourth human alpha isoform. This was accomplished by cloning the cDNA from human testis libraries and expressing it in HeLa cells. Sequence analysis demonstrates that the deduced amino acid sequence shares high homology with the other three human alpha isoforms and the rat alpha 4 isoform. Using an alpha 4 specific antibody, a protein ~100 kDa was identified through western blotting and it was localized to the flagellum of the sperm by immunohistochemistry. These results confirm the existence of the human alpha 4 Na+, K+-ATPase isoform and its localization to sperm suggest that the human alpha 4 isoform plays a role in the function human sperm.