A New Glow Peak, in Rhodopseudomonas Sphaeroides

A new glow peak at 120 K has been observed in Rhodopseudomanas sphaeroides and in its carotenoidless green mutant. This peak (labelled Zn), which is composed of two peaks at 120 and 150 K, appears when the bacteria are illuminated with white light while being cooled to 77 K and then warmed in darkness at a heating rate of 10 K per min. Delayed light emission and prompt fluorescence spectra show peaks around 530, 610 and 660 nm. The action spectra of light emission show a major peak at 410 nm and a smaller peak around 545 nm. The pigment responsible for the light emission is also leached out in the suspension medium. The chromophore responsible for the light emission appears to be magnesium protoporphyrin IX, not bacteriochlorophyll.