Abstract:
The distribution of excitation energy between the two
photosystems (PSII and PSI) of photosynthesis is regulated by the
light state transition. Three models have been proposed for the
mechanism of the state transition in phycobilisome (PBS) containing
organisms, two involving protein phosphorylation. A procedure for
the rapid isolation of thylakoid membranes and PBS fractions from
the cyanobacterium Synechococcus m. PCC 6301 in light state 1 and
light state 2 was developed. The phosphorylation of thylakoid and
soluble proteins rapidly isolated from intact cells in state 1 and state
2 was investigated. 77 K fluorescence emission spectra revealed that
rapidly isolated thylakoid membranes retained the excitation energy
distribution characteristic of intact cells in state 1 and state 2.
Phosphoproteins were identified by gel electrophoresis of both
thylakoid membrane and phycobilisome fractions isolated from cells
labelled with 32p orthophosphate. The results showed very close
phosphoprotein patterns for either thylakoid membrane or PBS
fractions in state 1 and state 2. These results do not support proposed
models for the state transition which required phosphorylation of
PBS or thylakoid membrane proteins.
