Photoinactivation of trypanothione reductase and glutathione reductase by A1-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 (AlPcS(4)) or hematoporphyrin (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 mu M Hp and 1.4-17 mu M AlPcS(4). The photosensitized irradiation modified the disulfide substrate-binding sites;af these enzymes, most likely the conserved catalytic histidine residue. In the dark, A1PcS, 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. (C)I996 Academic Press, Inc.