The phycobiliproteins of cyanobacteria or red algae in liquid
cultures became bleached after a brief exposure to temperatures
higher than 60 ~ C. Figure 1 A shows the visible absorption
spectra of Anacystis cells before and after heating for
8 rain at 65 ~ C. The absorption band centered at 623 nm was
greatly decreased following heating. The difference spectrum
obtained by subtracting the absorbance of heated cells from
the absorbance of unheated controls showed a large, asymmetrical
peak centered at 623 nm (Fig. 113). This difference
spectrum appeared virtually identical to the absorption spectrum
of intact phycobilisomes isolated from Anacystis
(Fig. 2 B). The small shoulder at 680 nm may reflect a slight (< 4%) bleaching of chlorophyll. We have extracted quantitatively
the lipid-soluble pigments (chlorophyll a and
carotenoids) from control and heat-treated cells. The difference
spectrum of the extracts showed that there was virtually
no loss in chlorophyll or carotenoid content during heat
treatment (data not shown). Apparently the bleaching of
phycobiliproteins was complete since the ratio of A623/A68o
in heat-treated cells was 0.26, which is in agreement with the
data obtained from thylakoid membranes free of phycobiliproteins
(Jones and Myers 1965; Myers et al. 1978).
Although cells were not viable after heat treatment, they
did not lose any pigments into the medium, and they appeared
morphologically the same before and after heating,
as viewed by light microscopy.