Absence Of H2 Research Articles

Hydrogen-stimulated CO2 fixation and coordinate induction of hydrogenase and ribulosebiphosphate carboxylase in a H2-uptake positive strain of Rhizobium japonicum

H2-uptake positive strains (122 DES and SR) and H2-uptake negative strains SR2 and SR3 of Rhizobium japonicum were examined for ribulosebisphosphate (RuBP) carboxylase and H2-uptake activities during growth conditions which induced formation of the hydrogenase system. The rate of 14CO2 uptake by hydrogenase-derepressed cells was about 6-times greater in the presence than in the absence of H2. RuBP carboxylase activity was observed in free-living R. japonicum strains 122 DES or SR only when the cells were derepressed for their hydrogenase system. Hydrogenase and RuBP carboxylase activities were coordinately induced by H2 and both were repressed by added succinate. Hydrogenase-negative mutant strains SR2 and SR3 derived from R. japonicum SR showed no detecyable RuBP carboxylase activities under hydrogenase derepression conditions. No detectable RuBP carboxylase was observed in bacteroids formed by H2-uptake positive strains R. japonicum 122 DES or SR. Propionyl CoA carboxylase activity was consistently observed in extracts of cells from free-living cultures of R. japonicum but activity was not appreciably influenced by the addition of H2. Neither phosphoenolpyruvate carboxylase nor phosphoenolpyruvate carboxykinase activity was detected in extracts of R. japonicum.

An ESR Study of an Al2O3-MoO3-CoO Catalyst in a System with H2 and Thio-β-naphthol

Abstract This work was planned in order to determine the reaction mechanism of the catalytic, direct desulfurization of organic sulfur compounds on the surface of Al2O3-MoO3-CoO particles. The experimental method consists of quantitative ESR measurements, by means of which the paramagnetic species on the surface of Al2O3, Al203-MoO3, and Al2O3-MoO3-CoO in the presence and in the absence of H2 and thio-β-naphthol were studied. As it is expected that, in an ideal and fast-reacting catalytic reaction system, no reaction intermediate can be found because it will be immediately converted to the final product, several artificial reaction systems were investigated in which either one of the reactants, catalyst components, or reaction conditions (e. g., temperature) was deficient. In such deficient systems, the reaction cycle is cut off and some intermediates are expected to accumulate. The paramagnetic species observed were Co3+, Mo5+, thio-β-naphthol+-O*2− or RS+H–O*2−, and some species formed on the surface of Al2O3, in the temperature region of 20°C–200°C. Mo6+ is concluded to be the electron trap to facilitate the formation of RS+H–O*2−, Co3+ is concluded to oxidize the Mo5+ thus formed to Mo6+, and Co2+ is concluded to reduce the R-S+H2–O*2− species. The latter then decomposes to H2S and R·.

Reaction of ethyl radicals with hydrogen and deuterium

Studies of the relative yields of C2H6 produced in the oxidation of propionaldehyde at 440°C in the presence and absence of H2 or D2 have enabled the velocity constant ratios k3/k14 and k5/k14 to be determined: C2H5+ C2H5CHO = C2H6+ C2H5CO (14) C2H5+ H2= C2H6+ H (5) C2H5+ D2= C2H5D + D (3) From the known values of k14, absolute values of k3 and k5 were obtained. By combining these values at 440°C with other values at lower temperatures, the best values for the velocity constants are k3= 4.07 × 109 exp (–14,700/RT), k5= 6.46 × 109 exp (–14,100/RT), in l. mole–1 sec–1 units.

Occurrence of Hydrogenase in Nitrogen-Fixing Organisms.

SummaryThe existence of hydrogenase, the enzyme activating molecular H2, has been demonstrated in cultures of Azotobacter by a methylene blue reduction method as well as by measurements of H2 uptake in the Warburg microrespirometer. The enzyme is found in cells grown in the presence or absence of H2 and using either free or combined nitrogen. Cells of the pea organism taken directly from the nodule possess the enzyme but those grown on the usual laboratory media do not.