Hydride transfer in liver alcohol dehydrogenase: quantum dynamics, kinetic isotope effects, and role of enzyme motion.

The quantum dynamics of the hydride transfer reaction catalyzed by liver alcohol dehydrogenase (LADH) are studied with real-time dynamical simulations including the motion of the entire solvated enzyme. The electronic quantum effects are incorporated with an empirical valence bond potential, and the nuclear quantum effects of the transferring hydrogen are incorporated with a mixed quantum/classical molecular dynamics method in which the transferring hydrogen nucleus is represented by a three-dimensional vibrational wave function. The equilibrium transition state theory rate constants are determined from the adiabatic quantum free energy profiles, which include the free energy of the zero point motion for the transferring nucleus. The nonequilibrium dynamical effects are determined by calculating the transmission coefficients with a reactive flux scheme based on real-time molecular dynamics with quantum transitions (MDQT) surface hopping trajectories. The values of nearly unity for these transmission coefficients imply that nonequilibrium dynamical effects such as barrier recrossings are not dominant for this reaction. The calculated deuterium and tritium kinetic isotope effects for the overall rate agree with experimental results. These simulations elucidate the fundamental nature of the nuclear quantum effects and provide evidence of hydrogen tunneling in the direction along the donor-acceptor axis. An analysis of the geometrical parameters during the equilibrium and nonequilibrium simulations provides insight into the relation between specific enzyme motions and enzyme activity. The donor-acceptor distance, the catalytic zinc-substrate oxygen distance, and the coenzyme (NAD(+)/NADH) ring angles are found to strongly impact the activation free energy barrier, while the donor-acceptor distance and one of the coenzyme ring angles are found to be correlated to the degree of barrier recrossing. The distance between VAL-203 and the reactive center is found to significantly impact the activation free energy but not the degree of barrier recrossing. This result indicates that the experimentally observed effect of mutating VAL-203 on the enzyme activity is due to the alteration of the equilibrium free energy difference between the transition state and the reactant rather than nonequilibrium dynamical factors. The promoting motion of VAL-203 is characterized in terms of steric interactions involving THR-178 and the coenzyme.

[Health status and morbidity in schoolchildren from villages in Silistra and Tutrakan Districts]. / Prouchvane na zdravnoto sustoianie i zabolevaemostta na uchenitsi ot niakoi sela na Silistrenski i Tutrakanski raion.

This is study of the health state and morbidity rate in a group comprising 408 schoolchildren from the Silistra and Tutrakan regions, aged 7 to 14 years. The results of the research demonstrate a slight lagging behind of the school-children's physical development relative to children of comparable ages from the urban areas. Their health state is estimated as good, and the somatic neurotic morbidity--rather low. The most frequently encountered affections include diseases of the upper airways, infectious and dental diseases. A considerable number of slightly hypochromic anemias are also recorded.

[Physiological hygienic characteristics of the teaching by the new educational programs for grade III]. / Khigienno-fiziologichna kharakteristika na obuchenieto po novite uchebnite programi v III klas.

The effect of the new training curricula and plans on the reactivity, health state and physical development of third-grade pupils is studied. Simultaneously with researches into the experimental class, investigations are conducted in a control class also. The working-capacity curve in the experimental-class pupils yields more clearcut fluctuations in a negative sense, interpreted as an expression of greater fatigue, as compared to the control class. This is confirmed by reliable data about the changes in the functional state of the higher nervous activity, hemodynamics and neuroendocrine regulation. It is concluded that the hygiene-physiological characteristics of the reactivity and health state of pupils, trained according to the new curricula, gives sufficient reason to stress the necessity of accurate assessment and rather prolonged medico-pedagogic observation with a view to obviate the cumulation of the described above negative effects on the organism of teenagers.