Functional characterization and periplasmic localization of a phosphorus starvation-induced alkaline phosphatase involved in phosphate acquisition in Pyropia yezoensis

Expression of the alkaline phosphatase gene in Pyropia yezoensis is transcriptionally induced under phosphorus deprivation. To elucidate its physiological role in phosphate acquisition, we purified the enzyme to homogeneity from phosphorus-starved thalli and characterized its biochemical properties. The alkaline phosphatase exhibited broad substrate specificity toward glycerophosphate, sugar phosphates, and nucleoside phosphates, and its activity was enhanced by Na+, Ca2+, and Mg2+ at concentrations comparable to those in natural seawater. Genomic analyses, together with biochemical characterization, revealed that the gene lacks introns and encodes an N-glycosylated phosphatase with a signal peptide. Immunological and biochemical analyses suggested that the mature 76-kDa enzyme is localized to the periplasm of phosphate-starved thalli. These findings suggest that P. yezoensis acquires phosphate under phosphorus-deficient conditions through a periplasmic alkaline phosphatase-mediated phosphate acquisition system.