Temperature dependence of photodynamic red cell membrane damage.

1. The protoporphyrin-sensitized photo-oxidation of free amino acids, amino acid residues in solubilized spectrin and amino acid residues in red blood cell membranes appeared to be virtually independent of temperature over the range 0-37 degrees C. The photodynamically produced increase in cation permeability in intact cells was also almost temperature independent. 2. The photodynamic cross-linking of the membrane proteins, on the other hand, was clearly temperature dependent, both when the proteins were present in the membrane structure and when isolated and purified. 3. With red cell membranes, illuminated in the presence of protoporphyrin at 0 degrees C, it could be shown that during subsequent incubation in the dark at 37 degrees C the protein cross-linking increased considerably. 4. The results indicate that cross-linking of membrane proteins is a secondary reaction in which rather stable photo-oxidation products of susceptible amino acid residues are involved. Furthermore, these experiments strongly suggest that the deterioration of membrane function, leading to increased caption permeability, is caused by photo-oxidation of amino acid residues rather than by cross-linking of membrane proteins.