Exposure of blue-green or red algal cells to temperatures
exceeding 60-65oC for several minutes resulted
in bleaching of all phycobilin absorption in the visible range,
with virtually no alteration in chlorophyll or carotenoid
absorption. Difference spectra of non-bleached vs bleached
cells appeared identical to absorption spectra of purified
phycobilisomes isolated from the same cell culture in high
phosphate medium. All phycobilin chromophores were
bleached at approximately the same rate during heating.
There were no changes in apparent molecular weights or
relative amounts of the phycobilisome apoproteins during
chromophore bleaching. Phycobilisomes in cell extracts
from Anacystis nidulans resisted bleaching when suspended
in medium of high phosphate concentration, but were
bleached at 60-65 oC within a few minutes when placed in
diluted medium. The results indicate that phycobilisomes in
vivo are stabilized by a mechanism other than high osmotic
and ionic strength. This represents a rapid and quantitative
method to characterize the phycobiliprotein content of
cyanobacteria and red algae in vivo.