Photoinactivation of trypanothione reductase and glutathione reductase by Al-phthalocyanine tetrasulfonate and hematoporphyrin.

The irradiation of Trypanosoma congolense trypanothione reductase (TR), human erythrocyte (HGR) and yeast glutathione reductase (YGR) with visible light in the presence of Al-phthalocyanine tetrasulfonate (A1PcS4) or hematoporphyrine (Hp) caused a time-dependent inactivation of these enzymes. TR was inactivated more rapidly than either HGR or YGR. Half-maximal rates of inactivation were determined in the presence of 100 microM Hp and 1.4-17 microM AlPcS4. The photosensitized irradiation modified the disulfide substrate-binding sites of these enzymes, most likely the conserved catalytic histidine residue. In the dark, AlPcS4 acted as a reversible inhibitor competitive with the disulfide substrate of TR and HGR. These findings suggest the possible use of photosensitized irradiation for preventing the transmission of trypanosomiasis by blood transfusion.