Tris Is a Competitive Inhibitor of K+ Activation of the Vacuolar H+-Pumping Pyrophosphatase.

The effects of a range of commonly used pH buffers on the hydrolytic activity of the plant vacuolar H+-transporting inorganic pyrophosphatase (V-PPase) from mung bean (Vigna radiata L.) hypocotyls were tested. All of the buffers inhibited K+ stimulation of the V-PPase, and the degree of inhibition was dependent on the concentrations of both the buffer and K+. The effects were dependent on the organic cation used in the buffers, and those tested inhibited in the order: Tris > Bis-Tris-propane > Bicine = Tricine > imidazole. Detailed studies revealed that a model in which Tris affects both the Km and Vmax for K+ stimulation provided an accurate description of the observed kinetics. The ability of different cations to stimulate the V-PPase was measured with a noncompeting buffer (5 mM imidazole-HCl) and the order of effectiveness was K+ = Rb+ > NH4+ >> Cs+ > Na+ > Li+, with the Km for K+ stimulation being about 1 to 2 mM. Published experiments performed in the presence of Tris were re-evaluated and all could be fitted to mixed inhibition kinetics, with kinetic parameters similar to those measured for the mung bean V-PPase. It is concluded that the variations in the published Km for K+ stimulation of the V-PPase are probably due to the effects of pH buffer cations and that the real value for this parameter is in the low millimolar range. The implications of this for regulation of the V-PPase by K+ in vivo and for the role of the enzyme in K+ transport into the vacuole are discussed

Ionospheric effects of the sudden stratospheric warming in 2009: Results of simulation with the first version of the EAGLE model

In this paper, we discuss perturbations in neutral temperature, total electron content (TEC), and critical frequency of the maximum of the F2 layer (foF2) during the sudden stratospheric warming in January 2009. The calculations were performed using the first version of the EAGLE (Entire Atmosphere Global Model), which is a combination of the models of the low--middle atmosphere (HAMMONIA) and the upper atmosphere (GSM TIP). The EAGLE reproduces observed stratospheric warming and related mesospheric cooling in the northern polar cap in January 2009. At thermospheric altitudes, the neutral temperature perturbations have a quasi-wave character with a wavelength of ∼40 km in the vertical direction. Our results indicate that the HAMMONIA model should be used in the EAGLE instead of the GSM TIP model for the neutral temperature calculations in the altitude region from 80 to 120 km. It is shown that the obtained model foF2 and TEC perturbations are mainly related to seasonal variations. The most-pronounced perturbations in the ionospheric electron density due to stratospheric warming are formed near the equator and are basically negative. Our analysis of the neutral temperature and electron density perturbations made it possible to conclude that the dependence of ionospheric parameters on seasonal changes in solar zenith angle is stronger than for the thermosphere parameters

Ionospheric Effects of the Sudden Stratospheric Warming in 2009: Results of Simulation with the First Version of the EAGLE Model

In this paper, we discuss perturbations in neutral temperature, total electron content (TEC), and critical frequency of the maximum of the F2 layer (foF2) during the sudden stratospheric warming in January 2009. The calculations were performed using the first version of the EAGLE (Entire Atmosphere Global Model), which is a combination of the models of the low–middle atmosphere (HAMMONIA) and the upper atmosphere (GSM TIP). The EAGLE reproduces observed stratospheric warming and related mesospheric cooling in the northern polar cap in January 2009. At thermospheric altitudes, the neutral temperature perturbations have a quasi-wave character with a wavelength of ∼40 km in the vertical direction. Our results indicate that the HAMMONIA model should be used in the EAGLE instead of the GSM TIP model for the neutral temperature calculations in the altitude region from 80 to 120 km. It is shown that the obtained model foF2 and TEC perturbations are mainly related to seasonal variations. The most-pronounced perturbations in the ionospheric electron density due to stratospheric warming are formed near the equator and are basically negative. Our analysis of the neutral temperature and electron density perturbations made it possible to conclude that the dependence of ionospheric parameters on seasonal changes in solar zenith angle is stronger than for the thermosphere parameters. © 2018, Pleiades Publishing, Ltd.The work was supported by the Russian Science Foundation (project no. 17-17-01060)