PubMed · 14834960
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J F A McMANUS. 1951. Practical histochemical methods for tissue pathology.. https://doi.org/10.1097/00007611-195104000-00011
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We determine conditions under which a random biochemical system is likely to contain a subsystem that is both autocatalytic and able to survive on some ambient 'food' source. Such systems have previously been investigated for their relevance to origin-of-life models. In this paper we extend earlier work, by finding precisely the order of catalysation required for the emergence of such self-sustaining autocatalytic networks. This answers questions raised in earlier papers, yet also allows for a more general class of models. We also show that a recently described polynomial-time algorithm for determining whether a catalytic reaction system contains an autocatalytic, self-sustaining subsystem is unlikely to adapt to allow inhibitory catalysation--in this case we show that the associated decision problem is NP-complete.
In situ microsensor measurements were combined with biogeochemical methods to determine oxygen, sulfur, and carbon cycling in microbial mats growing in a solar saltern (Salin-de-Giraud, France). Sulfate reduction rates closely followed the daily temperature changes and were highest during the day at 25 degrees C and lowest during the night at 11 degrees C, most probably fueled by direct substrate interactions between cyanobacteria and sulfate-reducing bacteria. Sulfate reduction was the major mineralization process during the night and the contribution of aerobic respiration to nighttime DIC production decreased. This decrease of aerobic respiration led to an increasing contribution of sulfide (and iron) oxidation to nighttime O2 consumption. A peak of elemental sulfur in a layer of high sulfate reduction at low sulfide concentration underneath the oxic zone indicated anoxygenic photosynthesis and/or sulfide oxidation by iron, which strongly contributed to sulfide consumption. We found a significant internal carbon cycling in the mat, and sulfate reduction directly supplied DIC for photosynthesis. The mats were characterized by a high iron content of 56 micromol Fe cm(-3), and iron cycling strongly controlled the sulfur cycle in the mat. This included sulfide precipitation resulting in high FeS contents with depth, and reactions of iron oxides with sulfide, especially after sunset, leading to a pronounced gap between oxygen and sulfide gradients and an unusual persistence of a pH peak in the uppermost mat layer until midnight.
The fluorescence properties of GFP are strongly influenced by the protonation states of its chromophore and nearby amino acid side chains. In the ground state, the GFP chromophore is neutral and absorbs in the near UV. Upon excitation, the chromophore is deprotonated, and the resulting anionic chromophore emits its green fluorescence. So far, only excited-state intermediates have been observed in the GFP photocycle. We have used ultrafast multipulse control spectroscopy to prepare and directly observe GFP's hidden anionic ground-state intermediates as an integral part of the photocycle. Combined with dispersed multichannel detection and advanced global analysis techniques, the existence of two distinct anionic ground-state intermediates, I(1) and I(2), has been unveiled. I(1) and I(2) absorb at 500 and 497 nm, respectively, and interconvert on a picosecond timescale. The I(2) intermediate has a lifetime of 400 ps, corresponding to a proton back-transfer process that regenerates the neutral ground state. Hydrogen/deuterium exchange of the protein leads to a significant increase of the I(1) and I(2) lifetimes, indicating that proton motion underlies their dynamics. We thus have assessed the complete chain of reaction intermediates and associated timescales that constitute the photocycle of GFP. Many elementary processes in biology rely on proton transfers that are limited by slow diffusional events, which seriously precludes their characterization. We have resolved the true reaction rate of a proton transfer in the molecular ground state of GFP, and our results may thus aid in the development of a generic understanding of proton transfer in biology.