The present invention provides compositions and methods for use in enzyme replacement therapy. The inventors disclose a method of producing membrane bound enzymes in an active soluble form by eliminating the glycosylphosphatidylinositol (GPI) membrane anchor. In particular the inventors disclose a soluble active form of the membrane bound enzyme TNSALP which they produced by deleting the GPI anchor single peptide sequence. They have further shown that this composition is useful for treatment of hypophosphatasia. The inventors also disclose oligo acid amino acid variants thereof which specifically target bone tissue.