ABSTRACT
It has been demonstrated that, within certain limits, the radiation of cultures of Paramecium bursaria, which had been kept in the dark, with wave-lengths greater than 3300 A., facilitates a subsequently elicited photodynamic response. A period of darkness following the pre-irradiation allows of a return to the normal condition. The role of radiation in the mechanism of photodynamic action is discussed.
The literature concerned with photodynamic action is surprisingly reticent upon the subject of the role played by the radiation used to induce the effect. It is tacitly assumed that the radiation, plays its part solely via the so-called ‘sensitizing’ agent. The possibility of direct action upon the test material appears to have been ignored. Recently (Calcutt, 1950), evidence has been put forward indicating that wavelengths greater than 3300 A. are effective in influencing the intracellular availability of sulphydryl groups. Additionally, it has been suggested that functional —SH groups are involved in the mechanism of photodynamic action (Calcutt, 1948). Further experimental work has been carried out to endeavour to elucidate this joint question of the role of radiation and —SH groups in photodynamic action.
