Month: September 2022

MORE WRENCHING THE SYSTEM. "In order to work so much more efficiently, some kind of redox switch seems to be required. It was suggested recently that this could involve a perturbation of the relative redox potentials of the core chlorophylls so that the chlorophyll cation may be distributed onto ChlD2, i.e. closer to the carotenoid." https://lnkd.in/dxpcWx8 View in LinkedIn

FUTILE CYCLE UTILITY. "When the cytochrome b 559 is already oxidized, the carotenoid cation can be reduced by chlorophyll, most likely ChlZD2, which is calculated to have a uniquely low potential. This branch of the futile cycle may serve as a trap for the cation and as a fluorescence quencher that will protect against over excitation of PSII." https://lnkd.in/dxpcWx8 View in LinkedIn

REMODELED VESTIGIAL MOLECULE. "All known photosynthetic reaction centres share the common structural feature of pseudo-C2 symmetry both at the level of the protein backbone and of the arrangement of the redox cofactors. This reflects their evolution from a common ancestral reaction centre which was made up of a homodimer of core protein subunits." https://lnkd.in/dxpcWx8 View in LinkedIn

PREVIOUSLY EFFICIENT. "The energy-converting enzymes evolved from ancestral enzymes that functioned in conditions of low O2 concentration or anaerobicity. These ancestral proteins did not have to deal with the inevitable side-reactions (leaks) that occur when O2 is present." https://lnkd.in/dxpcWx8 View in LinkedIn

ANCIENT WORK-AROUNDS. "The energy-converting redox enzymes perform productive reactions efficiently despite the involvement of high energy intermediates in their catalytic cycles. This is achieved by kinetic control: with forward reactions being faster than competing, energy-wasteful reactions. This requires appropriate cofactor spacing, driving forces and reorganizational energies." https://lnkd.in/dxpcWx8 View in LinkedIn

DELICATE BALANCE. "The energy wasteful reactions are a particular problem for photosynthetic reaction centres because the photochemistry gives such high energy intermediates. This problem is mainly dealt with through kinetic control: i.e. the forward reactions are faster than the back reactions. This is achieved by having cofactors appropriately spaced within the protein to allow rapid vectorial electron transfer across the membrane, separating the positive and negative charges from each other." https://lnkd.in/dxpcWx8 View in LinkedIn

BOLT-ON SOLUTIONS. "These features evolved in ancestral enzymes in a low O2 environment. When O2 appeared, energy-converting enzymes had to deal with its troublesome chemistry. Various protective mechanisms duly evolved that are not directly related to the enzymes’ principal redox roles." https://lnkd.in/dxpcWx8 View in LinkedIn

FINGER IN THE DYKE. "The tuning of electron transfer needed to deal with leaks and damaging back-reactions seems to be a requirement associated with life in the presence of oxygen." https://lnkd.in/dxpcWx8 View in LinkedIn

MODERN SYSTEM INEFFICIENCY. "These protective mechanisms involve fine-tuning of reduction potentials, switching of pathways and the use of short circuits, back-reactions and side-paths, all of which compromise efficiency." https://lnkd.in/dxpcWx8 View in LinkedIn

BAND AIDS AND BANDAGES. "These two basic characteristics pinpoint one of the main challenges encountered by these enzymes: how to favour the energy-productive processes over competing reactions in which the high energy intermediates decay without going through the useful energy converting step(s). In other words, to be efficient they must avoid back-reactions, short-circuits, by-passes, side-reactions, futile cycles and leaks." https://lnkd.in/dxpcWx8 View in LinkedIn