STUDIES OF PHOTODYNAMIC ACTION III. THE DIFFERENCE IN MECHANISM BETWEEN PHOTODYNAMIC

Dyes which bring about photodynamic hemolysis, in many instances, bring about the same effect in the absence of light (Dunkelwirkung), when the dye ispresentin sufficientlyhigh concentration.This sug gests the possibility that a reaction of the dye with cell constituents which is independent of light underlies the hemolysis; and that this reaction is accelerated by the activation of dye molecules by absorbed radiation,withtheresulthathemolysisoccursin lowerconcentrations of the dye. Certain rough correlations between the effect of the non irradiateddyes and thephotodynamiceffectshave been pointedout by Jodlbauer and Haffner (1921a) and by Blum (1930b) which would supportthisthesis,but itispossiblethathemolysisisinitiatedby en tirely different mechanisms in the two cases. Photodynamic hemolysis has been shown to require the presence of molecular oxygen (Hassel balch,1909;Schmidt and Norman, 1922),and thereseems littledoubt thatthisphenomenon isdependentupon oxidationsby molecularoxygen activated in some way by light. Obviously, if the hemolysis produced by thenon-irradiateddye isdependentupon thesame reactions,itmust likewise be inhibited by the absence of molecular oxygen. The attempt to separatethetwo processeson thisbasishas been the objectof the following experiments. ExPERIMENTAL Quantitative experimental treatment of this problem meets with various difficulties. Measurenient and comparison of the oxygen con sumption during hemolysis by irradiated and non-irradiated dyes meets the a priori objection that certain dyes greatly alter the normal metabol ism of cells without apparent destructive effects (see Barron and Hoff man, 1930), which might result in false conclusions as to the oxygen consumption of the process leading to hemolysis. Reducing the partial pressure of oxygen in any way, with the object of studying the effect on the hemolytic process, brings about changes in hydrogen ion concentr