Molecular basis of photoprotection and control of photosynthetic light-harvesting

In order to maximize their use of light energy in photosynthesis, plants have molecules that act as light-harvesting antennae, which collect light quanta and deliver them to the reaction centres, where energy conversion into a chemical form takes place. The functioning of the antenna responds to the extreme changes in the intensity of sunlight encountered in nature. In shade, light is efficiently harvested in photosynthesis. However, in full sunlight, much of the energy absorbed is not needed and there are vitally important switches to specific antenna states, which safely dissipate the excess energy as heat. This is essential for plant survival, because it provides protection against the potential photo-damage of the photosynthetic membrane. But whereas the features that establish high photosynthetic efficiency have been highlighted, almost nothing is known about the molecular nature of the dissipative states. Recently, the atomic structure of the major plant light-harvesting antenna protein, LHCII, has been determined by X-ray crystallography. Here we demonstrate that this is the structure of a dissipative state of LHCII. We present a spectroscopic analysis of this crystal form, and identify the specific changes in configuration of its pigment population that give LHCII the intrinsic capability to regulate energy flow. This provides a molecular basis for understanding the control of photosynthetic light-harvesting.     

The behavior of alloxan in the Hill reaction

Summary Hill activity induced by alloxan is characterized by non-stoichiometric oxygen evolution and cyclic electron flow due to autoxidation of dialuric acid and alloxantin, the reduction products of alloxan.     

Mitochondrial DNA deletions in human brain: regional variability and increase with advanced age.

We have examined the role of somatic mitochondrial DNA (mtDNA) mutations in human ageing by quantitating the accumulation of the common 4977 nucleotide pair (np) deletion (mtDNA4977) in the cortex, putamen and cerebellum. A significant increase in the mtDNA4977 deletion was seen in elderly individuals. In the cortex, the deleted to total mtDNA ratio ranged from 0.00023 to 0.012 in 67-77 year old brains and up to 0.034 in subjects over 80. In the putamen, the deletion level ranged from 0.0016 to 0.010 in 67 to 77 years old up to 0.12 in individuals over the age of 80. The cerebellum remained relatively devoid of mtDNA deletions. Similar changes were observed with a different 7436 np deletion. These changes suggest that somatic mtDNA deletions might contribute to the neurological impairment often associated with ageing.     

Biological activities of pure prostaglandins

Prostaglandins, the hydroxy unsaturated C20 fatty acids, are found throughout the body and have an equally wide range of biological activities. Prostaglandins are known to: 1) stimulate uterine contraction; 2) inhibit spontaneous contraction of the rabbit uterus; 3) inhibit the respiratory smooth muscle of different animals; 4) lower systemic arterial blood pressure when injected intravenously; 5) stimulate contractions in isolateral segments of intestinal smooth muscle of most species investigated; 6) produce transient sedation when intravenously injected in cats, and 7) inhibit lipolysis induced by catechal amines, corticotrophin, glucagon and thyroid stimulating hormone. The inhibitory and excitatory effects of prostaglandins may each have a physiological importance at different sites. Current state of knowledge of the distribution, metabolism and actions of the prostaglandins is still fragmentary. The functional significance of the prostaglandins is yet to be determined.