Three phosphohydrolase enzymes of bovine intestinal mucosa, alkaline phosphatase (ALPase), 5'-nucleotide phosphodiesterase (PDase), and 5'-nucleotidase seem to be structurally related because they are all immunologically cross-reactive independent of their oligosaccharide content. ALPase and PDase are quite similar in their catalytic mechanisms, and may be considered to constitute a "family" of related serine phosphohydrolases analogues to the serine proteases. We propose to compare structural details of ALPase and PDase to find just how similar they are. We plan to sequence the active sites of oligosaccharide-containing peptides of both enzymes. The active site peptides have been radioisotope labelled and purified, but sequencing them is difficult because they occur at the amino terminus, which is blocked so that automated sequencing is not possible. We also plan to compare ALPase and DPase, using immunological and affinity chromatography techniques, with ALPase and PDase from other tissues and organisms, and will be looking for other related proteins in the bovine intestinal mucosa.