Back-conversion

Biological exposure pathway of sulfur movement in soils of forest ecosystems is related to microbial transformation of sulfolipids. Back conversion of sulfate-S into organic matter immobilizes the anion and potentially reduces soil cation leaching. Processes of sulfur mineralization and incorporation proceed rapidly in response to several factors, including temperature, moisture, and exogenous sulfate availability in soils and water. 

The enzymes involved in the polyamine metabolic pathway have been the subject of intensive study, and a number of specific inhibitors for these enzymes have been designed as potential antitumor or antiparasitic agents [166]. Thus, a-difluoromethylornithine, has become a clinically useful agent [167]. Most of the studies involving inhibitors of polyamine metabolism have focused on enzymes involved in the biosynthetic pathway. Recently, there has been considerable interest generated in the enzyme spermidine/spermine-hT -acetyltrans-ferase enzyme (SSAT), the rate-limiting step in the back conversion of polyamines. SSAT, in conjunction with polyamine oxidase (PAO), allows for reversal of the biosynthetic pathway and attenuation of the levels of individual polyamines. 

The overall selectivity of the F-T process is intimately related to the production of methane, which is not economic, since the back conversion to... 

A quite different set of dynamic high-pressure techniques are based on the use of chemical or nuclear explosions to produce transient shock waves of high peak pressure but short duration. With such methods, one can often penetrate the high-T, P regions where kinetic barriers become unimportant and a catalyst is unnecessary. However, the same kinetics that allows facile conversion of graphite to diamonds as the shock front arrives also allows the facile back-conversion as the shock wave passes. As a pioneer of shock-wave diamond synthesis remarked ruefully, We were millionaires for one microsecond [B. J. Alder and C. S. Christian. Phys. Rev. Lett. 7, 367 (1961) B. J. Alder, in W. Paul and D. M. Warschauer (eds). Solids under Pressure (McGraw-Hill, New York, 1963), p. 385]. 

An attractive scheme for photogeneration of H2 (and 02) is via dye-sensitized redox reactions. Here the aim is to photogenerate the reduced relay A- which spontaneously reacts with water to give H2. The back conversion of the oxidised dye S+ to S may be achieved with a sacrificial donor D in a competitive reaction with A-... 

The back conversion of S+ into S may be achieved by sacrificing a donor D (through irreversible oxidation) added to the solution... 

Constant-volume conditions are often inconvenient and sometimes impossible to achieve. Most reactions occur under conditions of constant pressure (usually atmospheric pressure). If such a reaction results in a net increase in the number of moles of a gas, then the system does work on the surroundings (expansion). This follows from the fact that the gas formed must push the atmosphere back. Conversely, if more gas molecules are consumed than are produced, work is done on the system by the surroundings (compression). 

FIGURE 18.27 Molecule-to-molecule conversion using SC molecular ions, (a) Motional (secular) frequency spectrum of a Be" " crystal containing cold Hj . (b) After exposure to HD gas, most ions are converted into H2D+. (c) Subsequent exposure to H2 gas leads to partial back-conversion of H2D b to Hj". According to the CCD images, loss of hydrogen molecular ions occurs, while Be" " loss is negligible. 

After secondary reforming it is important to reduce the amount of carbon monoxide by way of the shift reaction. A very low level is required because on modern plant any carbon monoxide entering the methanators is converted back to methane to avoid carbon monoxide poisoning of the ammonia synthesis catalyst. This back conversion (a) uses three moles of hydrogen for every mole of carbon monoxide. 

Quasi-PM is somewhat different, in that it does not match the effective indices of the waveguide modes. Instead, the nonlinearity is turned off after one coherence length (i.e., = 0), preventing the back-conversion into the fundamental. 

FIGURE 9 Second-harmonic power development during propagation for non-phase-matched, perfectly phase-matched, and quasi-phase-matched (QPM) second-harmonic generation. For QPM, the back-conversion into the fundamental is prevented by turning off the nonlinearity every other coherence length. 

There are several modifications of the classical ATRP, such as an additional route of back conversion of Cu to Cu, which allows the reduction of the total amount of Cu used to the level of a few parts per million. 

Once produced, such nonequilibrium mixture can be stored at room temperature for days and even longer without significant back-conversion in the absence of paramagnetic materials [18]. 

Abstract The copper-dependent amine oxidases (CuAOs) and flavin-containing polyamine oxidases (PAOs) are involved in polyamine (PA) catabolic processes. Studies on plant CuAOs are still incomplete, whereas research on plant PAOs has advanced significantly in the past decade. The maize PAO, the best smdied plant PAO, and the barley PAOs were shown to catalyze PAs in a terminal catabolic pathway. Therefore, plant PAOs were assumed to have terminal catabolic activity, which differs from the back-conversion activity of mammalian PAOs. However, plant PAOs that have back-conversion activity are now reported. Here, studies on PAOs from the two model species Arabidopsis thaliana and Oryza sativa are compiled, and research on CuAOs is updated. Our current understanding of the roles of PAOs and CuAOs in plant development and defense responses is described. 

Keywords Arabidopsis thaliana, back-conversion pathway Copper-dependent amine oxidase Oryza sativa, plant, polyamine oxidase Terminal catabolism pathway... 

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