Studies on the Second Emerson Effect in the Hill Reaction in Algal Cells

This paper shows that the “second Emerson effect”¹ exists not only in photosynthesis, but also in the quinone reduction (Hill reaction), in Chlorella pyrenoidosa and Anacystis nidulans. The peaks at 650 mμ, 600 mμ, 560 mμ, 520 mμ, and 480 mμ, observed in the action spectrum of this effect in the Hill reaction in Chorella, are attributable to chlorophyll b; the occurrence of an additional peak at 670 mμ, 620 mμ, and of two (or three) peaks in the blueviolet region suggests that (at least) one form of chlorophyll a contributes to it. In analogy to suggestions made previously in the interpretation of the Emerson effect in photosynthesis, these results are taken as indicating that excitation by light preferentially absorbed by one (or two) forms of chlorophyll a (Chl a 690 + 700), needs support by simultaneous absorption of light in another form of chlorophyll a (Chl a 670)—directly or via energy transfer from chlorophyll b—in order to produce the Hill reaction with its full quantum yield. In Anacystis, the participation of phycocyanin in the Emerson effect in the Hill reaction is revealed by the occurrence, in the action spectrum of this effect, of peaks at about 560 mμ, 610 mμ, and 640 mμ; a peak at 670 mμ, due to Chl a 670, also is present.