Abstract
Plasma membrane (PM)-rich fractions were isolated from the foliose thallus (gametophyte) and filamentous thallus (sporophyte) of Porphyra yezoensis and assayed for vanadate-sensitive ATPase activities. NaCl-dependency for maximum activation and high optimum pH of the enzyme suggested the P. yezoensis PM had a Na+-ATPase. The PM ATPase activity in the sporophyte was much higher than that in the gametophyte. Immunoblotting analysis of PM proteins using a P-type ATPase-specific antiserum showed large accumulation of a 115-kDa protein in the sporophyte PM. EST sequences that were detected by similarity search against the P. yezoensis EST dataset using several consensus amino acid sequences in the P-type ATPase were used for in silico cloning. A protein sequence of 1144 amino acids with a molecular weight of 125851, which was predicted to be a Na+-ATPase by motif analysis and comparison with several P-type ATPases, was inferred by conceptual translation of the tentative nucleotide sequence.
