A 192-heme electron transfer network in the hydrazine dehydrogenase complex.

Anaerobic ammonium oxidation (anammox) is a major process in the biogeochemical nitrogen cycle in which nitrite and ammonium are converted to dinitrogen gas and water through the highly reactive intermediate hydrazine. So far, it is unknown how anammox organisms convert the toxic hydrazine into nitrogen and harvest the extremely low potential electrons (-750 mV) released in this process. We report the crystal structure and cryo electron microscopy structures of the responsible enzyme, hydrazine dehydrogenase, which is a 1.7 MDa multiprotein complex containing an extended electron transfer network of 192 heme groups spanning the entire complex. This unique molecular arrangement suggests a way in which the protein stores and releases the electrons obtained from hydrazine conversion, the final step in the globally important anammox process.

Bacterial Electron Transfer Chains Primed by Proteomics.

Electron transport phosphorylation is the central mechanism for most prokaryotic species to harvest energy released in the respiration of their substrates as ATP. Microorganisms have evolved incredible variations on this principle, most of these we perhaps do not know, considering that only a fraction of the microbial richness is known. Besides these variations, microbial species may show substantial versatility in using respiratory systems. In connection herewith, regulatory mechanisms control the expression of these respiratory enzyme systems and their assembly at the translational and posttranslational levels, to optimally accommodate changes in the supply of their energy substrates. Here, we present an overview of methods and techniques from the field of proteomics to explore bacterial electron transfer chains and their regulation at levels ranging from the whole organism down to the Ångstrom scales of protein structures. From the survey of the literature on this subject, it is concluded that proteomics, indeed, has substantially contributed to our comprehending of bacterial respiratory mechanisms, often in elegant combinations with genetic and biochemical approaches. However, we also note that advanced proteomics offers a wealth of opportunities, which have not been exploited at all, or at best underexploited in hypothesis-driving and hypothesis-driven research on bacterial bioenergetics. Examples obtained from the related area of mitochondrial oxidative phosphorylation research, where the application of advanced proteomics is more common, may illustrate these opportunities.

Nonadiabatic coherent evolution of two-level systems under spontaneous decay.

In this Letter we extend current perspectives in engineering reservoirs by producing a time-dependent master equation leading to a nonstationary superposition equilibrium state that can be nonadiabatically controlled by the system-reservoir parameters. Working with an ion trapped inside a nonideal cavity, we first engineer effective interactions, which allow us to achieve two classes of decoherence-free evolution of superpositions of the ground and excited ionic levels: those with a time-dependent azimuthal or polar angle. As an application, we generalize the purpose of an earlier study [Phys. Rev. Lett. 96, 150403 (2006)10.1103/PhysRevLett.96.150403], showing how to observe the geometric phases acquired by the protected nonstationary states even under nonadiabatic evolution.

Diffusion of calcium through dentin.

The purpose of this research was to investigate whether calcium ions from a paste of calcium hydroxide [Ca(OH)2] and saline introduced into root canals diffuse through the dentin to reach the surface of the root. Six teeth were opened and submitted to a biomechanical process, after which all the smear layer was removed. The experiment was divided into three phases: dissolution, dissolution and diffusion I, and dissolution and diffusion II. Dissolution-each tooth, with no Ca(OH)2 paste in place, was sealed both cervically and apically and stored in 700 ml of deonized water until calcium losses from the tooth into the water were stabilized. Dissolution and diffusion I-each root canal was filled with a paste of Ca(OH)2 and saline, sealed again apically and cervically, and returned to its solution. Dissolution and diffusion II-samples were divided into three parts: the control group or group 1, containing the original paste; group 2, in which the existing paste was diluted and the teeth were resealed and replaced in their solutions; and group 3, in which the existing paste was removed and a fresh paste was introduced. The diffusion was greater in group 3, followed by group 2. In the control group, we found a diffusion of calcium, which is statistically null. The results showed that calcium diffusion was observed, in the first 16 days, in all situations in which there was Ca(OH)2 paste inside the root canals.

The standardized stop: a new concept in endodontics.

This article presents a technique for making and using disposable standardized silicone stops. The stops have several diameters, colors, and thicknesses in order to make nonsurgical endodontics more efficient and improve the quality of therapy.