ABSTRACT
Ouabain-sensitive Na+,K+-ATPase activity, highly distributed in the plasma membrane fraction, was detectable in unfertilized eggs,scarcely altered in pre-hatching period and began to increase at the mesenchyme blastula corresponding stage. The activity reached to a maximum at the gastrula corresponding stage and thereafter decreased gradually. The activity was also found to be highest in ectoderm cells.
Inhibition of transcription by actinomycin D after the mesenchyme blastula stage did not affect the ATPase activity, while the inhibition between the hatching and the mesenchyme-blastula stages prevented the increase of the activity.
cDNA clone for Na+, K+-ATPase -subunit hybridized to about 5 Kb mRNA, which was maximally expressed at the mesenchyme blastula stage. A comparison of deduced amino acid sequences of this clone with transport ATPases of diverse species allowed the identification of the sequences that may form phosphorylation site, FITC-binding site, FSBA-binding sites and ouabain-binding sites.
