Molecular and Structural Level: Protein Phosphorylation
Cellular Level: Redox Control
Co-ordination of levels of adaptation: Imaging Chlorophyll Fluorescence
Redox is short for "reduction and oxidation", and describes the class of chemical reactions that involve transfer of electrons or hydrogen atoms. Redox reactions are fundamental to the way in which all cells obtain, convert, and use energy.
Photosynthesis converts the energy of sunlight into chemical form. Photosynthesis is a series of light-driven redox reactions, one of which involves a single molecule of the green pigment chlorophyll. In plant cells, photosynthesis occurs in chloroplasts, and uses water as a source of hydrogen atoms. This natural, chemical oxidation of water produces and replenishes the oxygen in the earth's atmosphere.
Respiration is the useful release of the energy that has been stored by photosynthesis. In animal and plant cells, respiration takes place in mitochondria, and is a series of redox reactions reactions that finally dump hydrogen atoms onto the oxygen molecules originally produced in photosynthesis. We depend totally on respiration and on photosynthesis - for the food we eat and the air we breathe.
|We study the structural changes of light-harvesting pigment-protein complexes as they undergo natural, chemical modification (phosphorylation) within the living cell. Directed mutation is used to alter specific structural features such as sites of phosphorylation. These structural changes regulate the conversion of light energy in photosynthesis, and this research may lead to an increased general understanding of control of protein-protein interactions in energy- and signal-transduction in biology.|
One of our central concerns is the way in which cells place the structure, function and synthesis of proteins under redox control - answerable to the energy-converting reactions of photosynthesis and respiration. We have recently resolved up to
seventeen chloroplast proteins whose phosphorylation is controlled by redox potential, and find parallel
control mechanisms in cyanobacteria, purple photosynthetic bacteria, and mitochondria. Chloroplasts and
mitochondria are descendants of bacteria, from which they retain genes for a small but constant sub-set of
their own components. We suspect that they have also inherited bacterial redox control systems to regulate
these genes. This hypothesis is currently being tested: we find that both protein phosphorylation and protein synthesis depend upon the redox potential of the medium in which isolated chloroplasts
and mitochondria are suspended.
A new technology of time-resolved imaging spectroscopy is applied to the study of cellular responses to
stress on different time scales and at different levels of gene expression. The natural fluorescence of
chlorophyll in photosynthetic systems is used as a non-invasive probe, by rapid computer acquisition of
digitized images of fluorescence. Variations in fluorescence of cells or individuals can then be measured simultaneously in large populations. Thus subtle, adaptive responses can be used for the first time as genetic markers
in screening for mutation.
|Chlorophyll fluorescence is light unused in photosynthesis; it varies as photosynthesis is regulated.|