Protoporphyrin-induced photodynamic effects on transport processes across the membrane of human erythrocytes

Previous studies have shown that illumination of erythrocytes with visible light in the presence of protoporphyrin results in cross-linking of membrane proteins and deterioration of several membrane functions, e.g. active transport of K⁺ and Na⁺.In the present study it is shown that carrier-mediated transport of glucose, l-leucine, sulphate and glycerol is also inhibited by the photodynamic process, whereas non-specific permeability of glycerol and thiourea is increased.It is shown that these effects are not caused by lipid peroxidation, but by photooxidation of membrane proteins. The inhibition of carrier-mediated transport is caused either by photodynamic oxidation of susceptible essential amino acid residues of the carrier molecules, or by an aspecific perturbation of the membrane structure, leading to inhibition of carrier functions.