PROTOPORPHYRIN‐SENSITIZED PHOTODYNAMIC MODIFICATION OF PROTEINS IN ISOLATED HUMAN RED BLOOD CELL MEMBRANES

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Abstract
Abstract— The photodynamic action of protoporphyrin on red cell ghosts is reflected by extensive cross‐linking of membrane proteins to very high molecular weight protein aggregates. This process was studied with sepharose gel chromatography and sodium dodecyl sulphate polyacrylamide gel electrophoresis.Most sensitive to this photodynamic effect are spectrin and band 2. 1, 2. 2, 2.3 and 4.1. polypeptides, which are cross‐linked after very brief illumination periods, with a concomitant loss of spectrin‐associated ATPase activity. Band 6 protein, representing the monomeric form of glyceraldehyde‐3‐phosphate dehydrogenase, is also very sensitive to protoporphyrin‐induced cross‐linking. The enzymatic activity decreased even faster than the amount of band 6 polypeptides, suggesting that modification(s) of the enzyme other than cross‐linking, possibly by rapid photooxidation of a thiol group, may be responsible for inactivation.Extracted and purified spectrin was cross‐linked with about the same velocity as membrane‐bound spectrin, reinforcing our previously drawn conclusion that membrane lipids are not involved in the cross‐linking reaction. Eluted band 6 polypeptides on the other hand exhibited a relatively fast photo‐oxidative modification but a much slower cross‐linking to dimers and tetramers. This suggests that the membrane structure, e.g. the spectrin matrix may play an essential role in the incorporation of membrane‐bound band 6 polypeptides in the high molecular weight cross‐linked complex.