title: Purification and characterization of a rat liver enzyme that hydrolyzes valaciclovir, the L-valyl ester prodrug of acyclovir.
abstract: Valaciclovir is an oral prodrug of the antiherpetic agent acyclovir. An enzyme that hydrolyzes valaciclovir to acyclovir, valaciclovir hydrolase (VACVase), was purified from rat liver and characterized. VACVase was a basic (pI 9.4) protein associated with mitochondria. It was monomeric and had a molecular mass of 29 kDa. Amino acid sequences of six VACVase peptides, including its NH2 terminus (13 amino acids) and accounting for approximately 20% of its complete sequence, were not found in the SwissProt protein data base. VACVase hydrolyzed other amino acid esters of acyclovir in addition to valaciclovir (kcat/Km = 58 mM-1 s-1), with a preference for the L-alanyl (kcat/Km = 226 mM-1 s-1) and L-methionyl (kcat/Km = 200 mM-1 s-1) esters. It did not hydrolyze other types of esters or numerous di- and tripeptides and aminoacyl-beta-naphthylamides. Hydrolysis of valaciclovir by VACVase was not inhibited by amastatin, antipain, aprotinin, bestatin, chymostatin, E-64, EDTA, ebelactone A, ebelactone B, elastatinal, leupeptin, pepstatin, or phosphoramidon. It was neither inhibited nor activated by Ca2+, Co2+, Mg2+, Mn2+, or Zn2+. Therefore, this enzyme is not a typical esterase or peptidase and, to our knowledge, it has not been described previously. Its physiological function is not known; however, it may play a significant role in the biotransformation of valaciclovir to acyclovir.
authors.affiliation: Division of Experimental Therapy, Burroughs Wellcome Co., Research Triangle Park, North Carolina 27709, USA.
authors.forename: T C
authors.initials: TC
authors.lastname: Burnette
authors.forename: J A
authors.initials: JA
authors.lastname: Harrington
authors.forename: J E
authors.initials: JE
authors.lastname: Reardon
authors.forename: B M
authors.initials: BM
authors.lastname: Merrill
authors.forename: P
authors.initials: P
authors.lastname: de Miranda
mesh_terms: D000212:Acyclovir / Q000031:analogs & derivatives* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D000998:Antiviral Agents / Q000378:metabolism*; D001711:Biotransformation; D006867:Hydrolases / Q000737:chemistry / Q000302:isolation & purification* / Q000502:physiology; D008099:Liver / Q000201:enzymology*; D008297:Male; D008969:Molecular Sequence Data; D011355:Prodrugs / Q000378:metabolism*; D051381:Rats; D000077483:Valacyclovir; D014633:Valine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D000998:Antiviral Agents; D011355:Prodrugs; D006867:Hydrolases; D014633:Valine; D000077483:Valacyclovir; D000212:Acyclovir