164 research outputs found
Cytochrome P450: taming a wild type enzyme
Protein engineering of cytochrome P450 monooxygenases
(P450s) has been very successful in generating valuable non-natural activities and properties, allowing these powerful catalysts to be used for the synthesis of drug metabolites and in biosynthetic pathways for the production of precursors of artemisinin and paclitaxel. Collected experience indicates that the P450s are highly ‘evolvable’ – they are particularly robust to mutation in their active sites and readily accept new substrates and exhibit new selectivities. Their ability to adapt to new challenges upon mutation may reflect the nonpolar nature of their active sites as well as their high degree of conformational variability
Ground states and dynamics of population-imbalanced Fermi condensates in one dimension
By using the numerically exact density-matrix renormalization group (DMRG)
approach, we investigate the ground states of harmonically trapped
one-dimensional (1D) fermions with population imbalance and find that the
Larkin-Ovchinnikov (LO) state, which is a condensed state of fermion pairs with
nonzero center-of-mass momentum, is realized for a wide range of parameters.
The phase diagram comprising the two phases of i) an LO state at the trap
center and a balanced condensate at the periphery and ii) an LO state at the
trap center and a pure majority component at the periphery, is obtained. The
reduced two-body density matrix indicates that most of the minority atoms
contribute to the LO-type quasi-condensate. With the time-dependent DMRG, we
also investigate the real-time dynamics of a system of 1D fermions in response
to a spin-flip excitation.Comment: 20 pages, 15 figures, accepted for publication in New Journal of
Physic
Responses to salt stress in Juncus acutus and J. maritimus during seed germination and vegetative plant growth
[EN] Responses to increasing salinity, during seed germination and vegetative plant growth, were studied in two related species of Juncus, J. maritimus and J. acutus. In both species, germination was optimal in the absence of salt, reduced by about 50% in the presence of 200 mM NaCl, and completely inhibited by NaCl concentrations above 300 mM. Previous exposure of the seeds to salt, up to 500 mM NaCl, did not affect the germination capacity in J. acutus, and clearly enhanced it in J. maritimus. A concentration-dependent inhibition of plant growth was observed in the presence of NaCl for both species, together with the parallel accumulation of sodium ions in the leaves, as determined by cation exchange HPLC. Regarding the levels of divalent cations, in J. acutus Ca2+ and Mg2+ increased up to about two-fold in plants treated with 500 mM NaCl, as compared to control plants, whereas in J. maritimus they were three-to four-fold higher than in J. acutus in the absence of salt, and did not change significantly with increasing NaCl concentrations. These results suggest that Ca2+ and Mg2+ participate in defence mechanisms against salt stress, which would be constitutive in J. maritimus and salt-inducible in J. acutus.Boscaiu Neagu, MT.; Ballesteros Amat, G.; Naranjo Olivero, MA.; Vicente Meana, Ó.; Boira Tortajada, H. (2011). Responses to salt stress in Juncus acutus and J. maritimus during seed germination and vegetative plant growth. Plant Biosystems. 145(4):770-777. doi:10.1080/11263504.2011.628446S770777145
High-Throughput Screening for Terpene-Synthase-Cyclization Activity and Directed Evolution of a Terpene Synthase
The development of high-throughput assays can be extremely
challenging, yet is essential for many applications in drug
discovery and enzyme engineering
Effect of supplemental Ca2+ on NaCl-stressed castor plants (Ricinus communis L.)
Greenhouse experiments were conducted to assess the effects of supplemental Ca2+ in salinised soil on germination and plant growth response of castor plant (Ricinus communis L. Var. Avani-31, Euphorbiaceae). NaCl amounting to 390 g was thoroughly mixed with soil of seven lots, of 100 kg each, to give electrical conductivity of 4.1 dS m–1. Further, Ca(NO3)2 × 4H20 to the quantity of 97.5, 195, 292.5, 390, 487.5, and 585 g was separately mixed with soil of six lots to give 1:0.25, 1:0.50, 1:0.75, 1:1, 1:1.25, and 1:1.50 Na+/Ca2+ ratios, respectively. The soil of the seventh lot contained only NaCl and its Na+/Ca2+ ratio was 1:0. Soil without addition of NaCl and Ca (NO3)2 × 4H20 served as control, with a 0:0 Na+/Ca2+ ratio. Salinity significantly retarded seed germination and plant growth, but the deleterious effects of NaCl on seed germination were ameliorated and plant growth was restored with Ca2+ supply at the critical level (1:0.25 Na+/Ca2+ ratio) to salinised soil. Supply of Ca2+ above the critical level further retarded seed germination and plant growth due to the increased soil salinity. Salt stress reduced N, P, K+ and Ca2+ content in plant tissues, but these nutrients were restored by addition of Ca2+ at the critical level to saline soil. In contrast, Na+ content in plant tissues significantly increased in response to salinity, but significantly decreased with increasing Ca2+ supply to saline soil. The results are discussed in terms of the beneficial effects of Ca2+ supply on the plant growth of Ricinus communis grown under saline conditions
Magnetic order in spin-1 and spin-3/2 interpolating square-triangle Heisenberg antiferromagnets
Using the coupled cluster method we investigate spin- -
Heisenberg antiferromagnets (HAFs) on an infinite, anisotropic, triangular
lattice when the spin quantum number or . With respect to a
square-lattice geometry the model has antiferromagnetic () bonds
between nearest neighbours and competing () bonds between
next-nearest neighbours across only one of the diagonals of each square
plaquette, the same one in each square. In a topologically equivalent
triangular-lattice geometry, we have two types of nearest-neighbour bonds:
namely the bonds along parallel chains and the
bonds producing an interchain coupling. The model thus interpolates
between an isotropic HAF on the square lattice at and a set of
decoupled chains at , with the isotropic HAF on the
triangular lattice in between at . For both the and the
models we find a second-order quantum phase transition at
and respectively,
between a N\'{e}el antiferromagnetic state and a helical state. In both cases
the ground-state energy and its first derivative are
continuous at , while the order parameter for the transition
(viz., the average on-site magnetization) does not go to zero on either side of
the transition. The transition at for both the and
cases is analogous to that observed in our previous work for the
case at a value . However, for the higher
spin values the transition is of continuous (second-order) type, as in the
classical case, whereas for the case it appears to be weakly
first-order in nature (although a second-order transition could not be
excluded).Comment: 17 pages, 8 figues (Figs. 2-7 have subfigs. (a)-(d)
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