Understanding the inefficiencies of Photosynthesis

Plants and photosynthetic bacteria capture light energy and convert it into stored chemical energy, which is used to drive reactions that convert water and carbon dioxide into the materials that almost all organisms on earth need to live and grow. Surprisingly the detailed mechanisms are not well understood. We employ a combination of spectroscopic methods and computational modelling to reveal pathways, mechanisms and rate limiting steps that control the light dependent and dark Photosynthetic reactions.

Dark Photosynthetic reactions

Inside plant cells, a network of enzymes creates organic carbon from the CO2 in the air and these reactions are strikingly inefficient. Typical enzymes can process ~1000 molecules per sec, but one of the enzymes, Rubisco, involved in the network, fixes only about 3 CO2 molecules per sec.
An understanding of Rubisco's inefficiency could clearly have significant impact, as it may provide a route to achieving profound improvements in photosynthetic efficiencies, through manipulating Rubisco in the chloroplast of higher plants.
This requires a range of quantitative approaches if the delivery of selected or engineered traits is to be a viable proposition. Prof David Klug, Prof Martin Parry and Dr Laura Barter have students working on quantitative proteomics, metabolomics, transcriptomics all allied with modelling and calculation to probe the Rubisco interactome and to investigate the regulatory networks controlling photosynthetic efficiency. The aim being to determine how these interactions control the up and down regulation of the enzyme.

Photosynthetic water splitting

The chloroplast houses a membrane which contains a chain of complexes involved with the intake of light energy and the transfer of charge across the membrane. This separation of charge is a method of storing energy and can be thought of as being like a battery, and therefore these complexes are the power-house of the organism.
It is striking that the plant is able to store enough energy, by creating stable intermediate states, to drive the energy demanding reactions that splits water and release oxygen as a by-product.
These reactions occur over timescales that cover more than fifteen orders of magnitude.
A range of spectroscopic methods in combination with modelling allow us to probe the quantitative structure function relationship. Single molecule spectroscopy has also been employed to probe properties of Photosynthetic complexes which are inaccessible in any other way. In particular the work has focused on the heterogeneity of the process and the dynamics associated with steps hidden by rate limiting steps in an ensemble experiment.

Two-Dimensional Infrared Spectroscopy

Current research includes the use of an optical analogue of 2D NMR to measure vibration-vibration coupling with the aim of probing the structure of enzyme active sites. Dr Laura Barter is particularly focusing on the water-splitting chemistry in Photosynthesis in collaboration with Prof David Klug and Dr Ian Gould in the Chemistry department.