Psoralen-sensitized photohemolysis: dependence on phстатья
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Аннотация:The effect of pH on psoralen-sensitized photohemolysis (irradiation at 366 nm, 23 W/m2) was investigated. The dose (D) dependence of the rate of photohemolysis (V) fitted V = V0 + kDx (where V0 is the rate of dark hemolysis and k is a coefficient). Variation of pH did not influence the exponent x, which was about 2; however, pH had a strong influence on the k value. The lowest V was observed in the pH interval from 8.0 to 8.4. It nearly doubled as the pH was changed from 8.4 to 9.0 as well as from 8.0 to 7.4. At pH below 7.4 the hemolysis rate increased sharply (by another factor of ∼4). Since psoralen does not contain acid/base groups, the effect of pH could hardly be a result of changing the photophysical properties of the sensitizer. The increase in V in the alkaline region could be attributed to more pronounced photooxidation of reduced glutathione as a substrate, while the jump at pH ∼7.3 would be ascribed to titration of a psoralen photooxidation product. The latter idea was supported by the HPLC data. Psoralen was preirradiated in ethanol and mixed in the dark with phosphate buffer at different pH, after which HPLC analysis revealed several pH-dependent photoproducts; for one of them the pH titration curve closely resembled the pH profile of psoralen-sensitized hemolysis.