Hydrogen transfer in catalysis by adenosylcobalamin-dependent diol dehydratase.

Studies [bachovchin, W. W., et al. (1978) Biochemistry 17, 2218] of the mechanism of inactivation of adenosylcobalamin-dependent diol dehydratase have led to the development of a general method to describe the kinetics of a reaction pathway containing a reservoir of mobile hydrogen. Analysis by this method of catalytic rate measurements for mixtures of 1,2-propanediol and 1,1-dideuterio-1,2-propanediol supports a mechanism involving an intermediate with three equivalent hydrogens, in which hydrogen transfer from this intermediate to product is the major rate-contributing step. Other results using tritium as a trace label [essenberg, M. K., et al. (1971) J. Am. Chem. Soc. 93, 1242] are considered in light of these deuterium isotope studies.     

HPA-axis activity in alcoholism: examples for a gene-environment interaction.

Genetic and environmental influences are both known to be causal factors in the development and maintenance of substance abuse disorders. This review aims to focus on the contributions of genetic and environmental research to the understanding of alcoholism and how gene-environment interactions result in a variety of addiction phenotypes. Gene-environment interactions have been reviewed by focusing on one of the most relevant environmental risk factors for alcoholism, stress. This is examined in more detail by reviewing the functioning of the hypothalamic-pituitary-adrenal (HPA) axis and its genetic and molecular components in this disorder. Recent evidence from animal and human studies have shown that the effects of stress on alcohol drinking are mediated by core HPA axis genes and are associated with genetic variations in those genes. The findings of the studies discussed here suggest that the collaborations of neuroscience, psychobiology and molecular genetics provide a promising framework to elucidate the exact mechanisms of gene-environment interactions as seen to convene upon the HPA axis and effect phenotypes of addiction.     

Spatial heterogeneity and dynamics of vernal phytoplankton species in the Baltic Sea in April-May 1986

The mesoscale phytoplankton distribution was studied as partof an international joint Baltic Sea Patchiness Experiment (PEX'86)during April–May 1986 in the open Baltic Proper. The studyperiod covered the peak phase of the phytoplankton spring bloom.The spatio-temporal dynamics of four dominating phytoplanktonspecies, Achnanthes taeniata, Chaetoceros spp., Skeletonemacostatum and Thalassiosira levanderi were studied within anarea of 20x40 nmi with grids of 2 and 4 nmi spatial resolution.The results showed highly varying spatial distributions forall species, and the variability was accentuated on the synopticspace scale before the development of the seasonal thermocline.The maxima of Chaetoceros spp. and Thalassiosira levanderi coincidedwith the anticyclonic and cyclonic eddies prevailing in thearea. Skeletonema costatum was found in high abundances onlywithin a warmer water mass of higher salinity advecting intothe area. The results pointed out that different successionalstages can simultaneously be found even in adjacent water massesand both the phytoplankton growth and composition during thebloom peak phase in the Central Baltic depend on complex factors,mainly those connected with mesoscale hydrodynamic features(eddies, frontal zones, jet currents).     

Evidence for the transport of manganous ion against an activity gradient by mitochondria

Mn²⁺ taken up by mitochondria through the often discussed energy dependent process has been previously shown to be separable by EPR spectroscopy into two spectral fractions (T. E. Gunter and J. S. Puskin, Biophys. J., 12 (1972) 625). One of these spectral fractions shows the characteristics of spin exchange. The other fraction, comprising roughly 10 % of the spectrally observed Mn²⁺, shows a hyperfine sextet.

Evidence is presented supporting the view that under conditions of maximum uptake of Mn²⁺ by the mitochondria in the absence of exogenous phosphate, the bulk of the hyperfine sextet fraction is in the Mn²⁺(H₂O)₆ form.

Spectral data is then used to show that if this view is correct, this fraction is found within mitochondria under conditions where it can be shown to have been accumulated against an activity gradient.

Spectral line width data for this fraction is interpreted in such a way as to provide an upper limit to intramitochondrial local viscosity where this hexahydrate form of manganese is present. This upper limit is approximately 1.5 cP at 37 °C and 0.25 M external osmolarity for example.     

Effect of u.v.-B irradiance on the response of 15N-nitrate uptake of Lauderia annulate and Synedra planctonica

The marine diatoms Lauderia annulata and Synedra planctonicaharvested during exponential growth were exposed to differentdoses of u.v.-B (286, 439 and 710 J m^–2 d^–1) for2 days. Uptake of ¹⁵N-nitrate was estimated before, during andafter u.v.-B radiation over 2 days. Exposure to high levelsof u.v.-B (710 J m^–2 d^–1) caused irreversible damageat the second daily irradiance. Lauderia cells were less affectedby u.v.-B stress than Synedra cells. ¹⁵N-nitrate uptake wasreduced under u.v.-B irradiance but could be reactivated within1 day following exposure to a low dose (286 J m^–2 d^–1).Higher levels of u.v.-B radiation (710 J m^–2 d^–1)led to irreversible damage. The pattern of ¹⁵N-incorporationinto several amino acids of Lauderia varied after 2 days ofu.v.-B radiation. ¹⁵N enrichment of glutamine increased markedlyafter u.v.-B stress (717 J m^–2 d^–1) whereas ^I5Nexcess of aspartic acid was significantly reduced. Results arediscussed with reference to the u.v.-B damage of the nitratetransport system.