Artificial control of enzyme reactions by the photoexcitation of hematoporphyrin adsorbed on living yeast cells

The objective of our research was to establish control of biological functi ons by the illumination of a photosensitizer of hematoporphyrin that was ex ternally provided in a biological system. We found using an ESR method that the reduction of 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPOL), as a reduction probe, caused by enzyme reactions can be controlled through the photoexcitation of hematoporphyrin adsorbed on the living yeast cells (HP/Yeast system). On the basis of the effects of some electron-transfer bl ockers through its reduction rate, it has been postulated that the reductio n of TEMPOL is mainly conducted through ferredoxin (ferredoxin-NAD(P)(+) re ductase), which could be controlled through the illumination of HP connecte d with a mitochondrial electron-transfer system. A possible mechanism for c ontrolling the reduction of TEMPOL is discussed in connection with the ener gy levels of HP and the redox potentials of the components in yeast cell pa rticipating in this phenomenon.