OPTICAL CONTROL OF ENZYMATIC CONVERSION OF SUCROSE TO GLUCOSE BY BACTERIORHODOPSIN INCORPORATED INTO SELF-ASSEMBLED PHOSPHATIDYLCHOLINE VESICLES

This report describes an alternative method to modulate enzyme activit y optically through pH modulation. Bacteriorhodopsin (BR) is used to r egulate the activity of an enzyme which it does not naturally regulate . In this study BR controlled the pH-dependent conversion of sucrose t o glucose by the enzyme, invertase. BR is oriented in the wall of phos phatidylcholine vesicles so that at pH values greater than 4-5 it pump s protons into the vesicles and at pH values less than 4 it pumps prot ons out of the vesicle when illuminated with light of the proper wavel ength. The bulk-solution pH correspondingly changes as a result. At an initial pH of 5.57 the change in pH of the solution due to pumping by the bacteriorhodopsin-vesicle complex was 0.17 pH units. To study thi s effect on the enzyme, samples containing BR vesicles and invertase w ere assayed for enzyme activity under dark and illuminated conditions. It was found that changes in enzyme activity, upon illumination, were generally larger than predicted for the corresponding changes in the bulk solution pH generated by the BR vesicles.