Removal of the PsaF Polypeptide Biases Electron Transfer in Favor of the PsaB Branch of Cofactors in Triton X‐100 Photosystem I Complexes from Synechococcus sp. PCC 7002†

Continuous wave (CW) and transient electron paramagnetic resonance studies have implied that when PsaF is removed genetically, the double reduction of A_1A is facile, the lifetime of A_1A^? is shorter and the ratio of fast to slow kinetic phases increases in PS I complexes isolated with Triton X‐100 (Van der Est, A., A. I. Valieva, Y. E. Kandrashkin, G. Shen, D. A. Bryant and J. H. Golbeck [2004] Biochemistry 43 , 1264–1275). Changes in the lifetimes of A_1A^? and A_1B^? are characteristic of mutants involving the quinone binding sites, but changes in the relative amplitudes of A_1A^? and A_1B^? are characteristic of mutants involving the primary electron acceptors, A_0A and A_0B. Here, we measured the fast and slow phases of electron transfer from A_1B^? and A_1A^? to F_X in psaF and psaE psaF null mutants using time‐resolved CW and pump‐probe optical absorption spectroscopy. The lifetime of the fast kinetic phase was found to be unaltered, but the lifetime of the slow kinetic phase was shorter in the psaF null mutant and even more so in the psaE psaF null mutant. Concomitantly, the amplitude of the fast kinetic phase increased by a factor of 1.8 and 2.0 in the psaF and psaE psaF null mutants, respectively, at the expense of the slow kinetic phase. The change in ratio of the fast to slow kinetic phases is explained as either a redirection of electron transfer through A_1B at the expense of A_1A, or a shortening of the lifetime of A_1A^? to become identical to that of A_1B^?. The constant lifetime and the characteristics of the near‐UV spectrum of the fast kinetic phase favor the former explanation. A unified hypothesis is presented of a displacement of the A‐jk(1) α‐helix and switchback loop, which would weaken the H‐bond from Leu₇₂₂ to A_1A, accounting for the acceleration of the slow kinetic phase, as well as weaken the H‐bond from Tyr₆₉₆ to A_0A, accounting for the bias of electron transfer in favor of the PsaB branch of cofactors.     

Dynamics of solitons in the fourth-order nonlocal nonlinear Schrödinger equation

Nonlinear Dynamics - We consider the fourth-order nonlocal nonlinear Schrödinger equation and generate the Lax pair. We then employ Darboux transformation to generate dark and antidark soliton...     

Electrically weak asymmetry in the elastic scattering of electrons by nuclei with multipole moments

The differential elastic-scattering cross section of longitudinally polarized electrons by nuclei of arbitrary spin and isospin is calculated in the Born approximation, taking into account the interference of electromagnetic interaction and the interaction of weak neutral currents. For a nucleus of spin J 3/2, explicit expressions are obtained for the interference terms in terms of the electromagnetic multipole form factors F_C, f_Q, f_M1 and f_M3. Using the example of the³He,¹¹B,¹⁹F and⁴⁰Ca nuclei, the behavior of electrically weak asymmetry of the cross section is investigated in detail in the framework of three gauge models. It is shown that the asymmetry of a_Rl is 10^–5 for E - 100 MeV, and is sensitive to the nuclear structure: By taking into account the contributions not only of the charge and magnetic-dipole scattering but also of the quadrupole and octupole scattering, one can obtain additional information on the structure of weak electron-nucleus interaction.This paper was presented at a conference on Investigations of Spin Phenomena in High-Energy Physics held at Protvino, November 23–26, 1982.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 79–84, April, 1984.     

Vector dark solitons with oscillating background density

Nonlinear Dynamics - The system of generalized coupled nonlinear Schrödinger equations is considered. Using Darboux transformation, a new class of vector dark soliton solutions is obtained....     

Nonlocal Solitons in a Nonlinear Chain of Atoms

Physics of the Solid State - A nonlinear 1D chain with nonlocal interaction has been considered. A nonlocal equation describing the propagation of envelope waves in the medium has been obtained...     

Nontrivial class of composite U(σ+μ) vector solitons

A mixed problem for the compact U(m) vector nonlinear Schrödinger model with an arbitrary sign of coupling constant is exactly solved. It is shown that a new class of solutions—composite U(σ+μ) vector solitons with inelastic interaction (changing shape without energy loss) at σ>1 and strictly elastic interaction at σ=1— exists for m≥3. These solitons are color structures consisting of σ bright and μ dark solitons (σ+μ=m) and capable of existing in both self-focusing and defocusing media. The N-soliton formula universal for attraction and repulsion is derived by the Hirota method.     

Reversible polarization of ferroelectric ceramics in a rapid-growing electric field

The complex permittivity of ferroelectric PZT ceramics with different compositions was measured in a pulsed rapid-growing electric field. The time dependence of the real component exhibits three peaks. The dips between them correlate with imaginary component peaks. Domain mechanisms that contribute to the ferroelectric polarization and are responsible for the time dependences are considered.