title: Reaction of rat liver DT-diaphorase (NAD(P)H:quinone acceptor reductase) with 5'-[p-(fluorosulfonyl)benzoyl]-adenosine.
abstract: Rat liver DT-diaphorase is inactivated by 5'-[p-(fluorosulfonyl)benzoyl]adenosine (5'-FSBA), following pseudo-first-order kinetics. A double-reciprocal plot of 1/kobs versus 1/[5'-FSBA] yields a straight line with a positive y intercept, indicative of reversible binding of the inhibitor before an irreversible incorporation. The dissociation constant (Kd) for the initial reversible enzyme-inhibitor complex is estimated at 2.86 mM with k2 = 0.22 min-1 (at pH 7.5 and 25 degrees). A stoichiometry of 2 mol of 5'-FSBA bound/mol of enzyme (i.e., 1 mol of the inhibitor bound/mol of subunit), at 100% inactivation, was determined from inactivation kinetics and from incorporation studies using 5'-[p-(fluorosulfonyl)benzoyl]-[14C]-adenosine. The irreversible inactivation as well as the covalent incorporation could be completely prevented by the presence of NAD(P)H during the incubation. These results indicate that 5'-FSBA inactivated DT-diaphorase by occupying its NAD(P)H binding site. Reverse phase high pressure liquid chromatography of tryptic digests of [14C]5'-FSBA-labeled DT-diaphorase revealed one radioactive peak containing two comigrating peptides. They are 146I-T-T-G-G-S-G-S-M-Y155 and 262S-I-P-A-D-N-Q-I-K270. By comparison of these sequences to those of the nucleotide binding sites of several kinases and dehydrogenases, it is suggested that the peptide I-T-T-G-G-S-G-S-M-Y is the one modified by 5'-FSBA and would be predicted to be the region where the pyrophosphate group of NAD(P)H binds.
authors.affiliation: Division of Immunology, Beckman Research Institute of the City of Hope, Duarte, California 91010.
authors.forename: X F
authors.initials: XF
authors.lastname: Liu
authors.forename: H
authors.initials: H
authors.lastname: Yuan
authors.forename: M
authors.initials: M
authors.lastname: Haniu
authors.forename: T
authors.initials: T
authors.lastname: Iyanagi
authors.forename: J E
authors.initials: JE
authors.lastname: Shively
authors.forename: S A
authors.initials: SA
authors.lastname: Chen
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000345:Affinity Labels / Q000494:pharmacology*; D000595:Amino Acid Sequence; D000818:Animals; D005260:Female; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D016660:NAD(P)H Dehydrogenase (Quinone); D010446:Peptide Fragments / Q000302:isolation & purification; D011808:Quinone Reductases / Q000037:antagonists & inhibitors*; D051381:Rats; D011919:Rats, Inbred Strains; D014357:Trypsin
chemical_list: D000345:Affinity Labels; D010446:Peptide Fragments; C010959:5'-(4-fluorosulfonylbenzoyl)adenosine; D016660:NAD(P)H Dehydrogenase (Quinone); D011808:Quinone Reductases; D014357:Trypsin; D000241:Adenosine