ACTION SPECTRUM FOR PALING (DECREASE IN REFRACTIVE INDEX) OF ULTRAVIOLET-IRRADIATED CHROMOSOME SEGMENTS

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Abstract
In producing paling (loss of nonaqueous material) in ultraviolet-irradiated segments of living chromosomes, the quantum effectiveness at wave-lengths 2,250, 2,400, 2,500, 2,600, 2,700, 2,800, and 3,000 A has the relative values 220, 30, 10, 16, 19, 16, and 22 respectively. Thus, the action spectrum more nearly parallels the absorption spectrum of a tyrosine-containing protein than that of DNA or any of its nucleotides. From this finding, along with observations by others that paling is accompanied by decrease in ultraviolet absorption, in Fuelgen reaction, and in Alfert-Geschwind reaction, it is concluded that paling is most likely due to loss of both protein and DNA, possibly as some combination of the 2 which is detached from the chromosome by photons absorbed by protein.