Abstract
The fourth derivative of absorption spectra between 260 and 310 nm were used for monitoring the changes in exposure of tyrosine and tryptophan side chains in cytochrome P-450 1A2 to solvent. Titration of the enzyme with a specific inhibitor, α-naphthoflavone (2-phenylazo[h]chromen-4-one) to inhibitor concentration of 30 μM resulted in small but pronounced changes in derivative spectra (decrease in the maximum amplitude, downshift of the spectral maximum at about 293 nm) corresponding to the exposure of tryptophans towards the solvent. Further addition of the inhibitor led to a decrease of the exposure of these aromatic side-chains. Similar behaviour was also observed in this work for other cytochromes P-450 (2B4 and 11A1). The fourth derivative of absorption spectra was also used to examine the stability of the enzyme both in the presence and absence of α-naphthoflavone, with increasing pressure (up to 400 MPa) and temperature (up to 35 °C) as pertubing factors. The results show that cytochrome P-450 1A2 has a stable conformation as all the conformational changes observed were (spectrally) fully reversible.
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