Alkaline phosphatase (EC 3.1.3.1) from bovine intestine mucosa (BIAP) is a homodimeric metalloenzyme, which hydrolyses nonspecifically phosphate monoesters at alkaline pH with release of inorganic phosphate and alcohol. BIAP is either soluble (sBIAP) or membrane-anchored by a glycosylphosphatidylinositol moiety (GPI-BIAP). This anchor might have some contribution in the stabilization of the GPI-linked protein structure. Our purpose was to study the role of the anchor by using two parameters, the enzymatic activity and the protein conformation, which was analyzed by using FTIR spectroscopy. We determined that the two forms of BIAP show some similarities with the previously described structure of alkaline phosphatase isolated from Escherichia coli and human placenta. Meanwhile GPI-BIAP and sBIAP exhibit similar specific activities, the presence of the anchor increases the thermal and pH stabilities of the enzyme activity and conformation. (C) 2002 Elsevier Science (USA).