Changes in plasma membrane protein structure after photodynamic action in freshly isolated rat pancreatic acini. An FTIR study

Photodynamic action of a plasma membrane-specific photosensitizer sulphonated aluminium phthalocyanine (SALPC) has been found to regulate cellular signalling pathways. The present study aimed to investigate whether SALPC photodynamic action modulates the structure of plasma membrane proteins, and as control, of model proteins. To check the photodynamic effect, intrinsic fluorescence of model proteins bovine serum albumin (BSA), phospholipase A2 (PLA2), and calmodulin were monitored continuously during photodynamic action (SALPC 1 μM, light 14,000 lx at >580 nm). Significant decrease in fluorescence intensity was observed in BSA and PLA2, whereas the fluorescence of calmodulin was not affected. Confirming a major change in protein structure, difference IR spectrum revealed a significant downward deflection after photodynamic action in both BSA and in pancreatic acinar cells, whereas SALPC alone or light illumination alone resulted in no major deflection. Quantitative FTIR analysis indicated that in BSA, photodynamic action decreased the content of α-helix, increased the content of β-turn and random structures, whereas β-sheet remained the same; in freshly isolated rat pancreatic acini, photodynamic action decreased the content of α-helix and β-sheet, increased the content of β-turn and random structures. Taken together the fact that under the present experimental conditions SALPC mainly localized at the plasma membrane, it is concluded that SALPC photodynamic action directly modulates plasma membrane protein structure.