BPHL is a member of the serine protease family. BPHL is expressed large quantities in liver and kidney and in minor quantities in heart, intestine and skeletal muscle. BPHL is a specific alpha-amino acid ester hydrolase that prefers small, hydrophobic, and aromatic side chains and does not have a stringent requirement for the leaving group other than preferring a primary alcohol. It catalyzes the hydrolytic activation of amino acid ester prodrugs of nucleoside analogs such as valacyclovir and valganciclovir. BPHL also activates valacyclovir to acyclovir. It may play a role in detoxification processes.