protocol.76 All reaction mixtures (final volume of 200 lL)
contained 160 lM NADPH, varying inhibitor concentrations,
P. falciparum TrxR (1.23 nmol), 2% DMSO in TrxR buffer at
25 ◦C. Inhibitor concentrations used were 0–0.5–1.0–2.0–5.0 lM
for 1,4-NQ and 0–0.5–1.0–2.0–3.0–4.0–5.0–20.0 lM for aza-
naphthoquinone 5. At different time points, 5 lL-aliquots of
each reaction mixture were removed and the residual activity was
measured in the standard Trx reduction assay at 25 ◦C (in the
presence of 24 lM Trx, 1 mM GSSG and 100 lM NADPH).
2% DMSO was used in control assays. From semi-logarithmic
plots ln(vi/v0) versus incubation time apparent rate constants
of irreversible inhibition (kobs) of the fraction of non-inhibited
enzyme activity versus [I] were fitted to eqn (2):
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(2)
where KI represents the dissociation constant of the inhibitor,
and ki is the first order rate constant for irreversible inactivation,
respectively.
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Acknowledgements
Our work is supported by the Centre National de la Recherche Sci-
entifique (E.D.C.) and by the Deutsche Forschungsgemeinschaft
via the SFB 544 “Control of Tropical Infectious Diseases,” project
B14 (E.D.C.) and the grant BE1540/4-4 (K.B.). T.B. is grateful to
the French “Ministe`re de l Education Nationale, de la Recherche
et de la Technologie” for a doctoral fellowship.
ꢁ
´
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