title: Metabolic transformation of AZTp4A by Ap4A hydrolase regenerates AZT triphosphate.
abstract: The reverse transcriptase (RT) of HIV which has been inhibited by the incorporation of AZT into the primer strand is subject to a deblocking reaction by cellular ATP. This reaction yields unblocked primer plus the dinucleoside tetraphosphate, AZTp(4)A. In the present study, we report that AZTp(4)A is an excellent substrate for the enzyme Ap(4)A hydrolase (asymmetrical dinucleoside tetraphosphatase, EC 3.6.1.17), an enzyme that is widely distributed in many cell types. Progress of the reaction has been monitored by 31P NMR, and it was found that hydrolysis results in the production of AZTTP:ATP in a 7:1 ratio. The AZTp(4)A was also hydrolyzed at a rate 1.8-fold more rapidly than Ap(4)A. Spectrophotometric assays yielded Michaelis constants of 2.35 and 0.71 microM for Ap(4)A and AZTp(4)A, respectively. It, therefore, appears that Ap(4)A hydrolase can play a useful role in the regeneration of the AZTTP, the active form of AZT, for the inhibition of HIV RT.
authors.affiliation: Department of Health and Human Services, Laboratory of Structural Biology, MR-01, National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709, USA.
authors.forename: Wayne H
authors.initials: WH
authors.lastname: Pitcher
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Kirby
authors.forename: Eugene F
authors.initials: EF
authors.lastname: DeRose
authors.forename: Robert E
authors.initials: RE
authors.lastname: London
mesh_terms: D017766:Acid Anhydride Hydrolases / Q000378:metabolism*; D001711:Biotransformation; D054306:Dideoxynucleotides; D054303:HIV Reverse Transcriptase / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D010759:Phosphorus Isotopes / Q000378:metabolism; D013942:Thymine Nucleotides / Q000378:metabolism*; D015215:Zidovudine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology
chemical_list: C477810:AZTp4A; D054306:Dideoxynucleotides; D010759:Phosphorus Isotopes; D013942:Thymine Nucleotides; D015215:Zidovudine; C052873:zidovudine triphosphate; D054303:HIV Reverse Transcriptase; D017766:Acid Anhydride Hydrolases; C020023:bis(5'-nucleosyl)tetraphosphatase (asymmetrical)