Lysis of resealed erythrocyte ghosts by photoactivated tetrapyrroles: estimation of photolesion dimensions.

1. Resealed erythrocyte ghosts containing Na+ and glucose-6-P (G6P) as markers of membrane integrity were used as a model system for probing the damaging effects of photoactivated tetrapyrroles on cell membranes. 2. Continuous blue-light irradiation of bilirubin (BR)-sensitized and protoporphyrin (PP)-sensitized ghosts made them progressively more permeable to Na+, the cation emerging well ahead of G6P. 3. G6P efflux occurred abruptly after a lag period and resembled an all-or-none process. 4. These and other results suggest that a relatively subtle structural modification (possibly in some crucial protein(s) is sufficient for Na+ release, whereas gross disruption of the bilayer (probably by free-radical lipid peroxidation) is necessary for G6P release. 5. The dimensions of the G6P-releasing photolesions were estimated by density floatation centrifugation, using saccharides of increasing molecular size. Both BR and PP produced pores greater than 11 A but less than 42 A in diam., which is considerable smaller than the size range estimated in hypotonically lysed ghosts.