Kinetics and mechanism of iron oxidation in apoferritin

The enzymatic activity of horse spleen apoferritin in iron(II) oxidation was examined using microelectrode oximetry. The reaction exhibits saturation kinetics with respect to both Fe\sp{2+} and O\sb2. The kinetics are discussed in terms of two mechanisms, one involving monomeric and the other dimeric iron protein complexes. In both instances Fe\sp{2+} oxidation occurs in 1-electron steps. At increments of 50 Fe\sp{2+}/protein or less, all of the iron is oxidized via the protein ferroxidase site(s), independent of the amount of core already present. The results of these studies emphasize the role of the protein shell in all phases of core growth. A detailed study of the kinetics of iron(II) oxidation by molecular oxygen in natural and recombinant human apoferritins has also been carried out to understand the ferroxidase activity of the protein shell and the function of the H and L subunits during iron uptake in ferritins. Zn\sp{2+} was shown to be a noncompetitive inhibitor of Fe\sp{2+} oxidation in rHF but a mixed inhibitor in HLF. These different forms of Zn\sp{2+} inhibition in the two proteins and the higher than expected activity of HLF based on its H-chain composition as well as differences in their enzyme kinetic parameters suggest that H and L-chains cooperate in modulating the ferroxidase activity of the apoferritin even though the L-subunit lacks a ferroxidase site itself. Additionally, the intermediate species produced in the process of ferritin reconstitution from apoferritin, Fe\sp{2+} and dioxygen, have been investigated using fast-mixing and stir-mixing freeze-quench techniques and EPR spectroscopy. The intermediate species found include the previously defined monomeric Fe\sp{3+}-protein complex (g\sp\prime = 4.3), the mixed-valence Fe\sp{2+}-Fe\sp{3+} intermediate (g\sp\prime = 1.87) and the free radical, as well as a new radical with axial magnetic symmetry. Interaction of Fe\sp{2+} with the monomeric Fe\sp{3+}-protein complex was demonstrated. A 1:1 relationship between the monomeric Fe\sp{3+}-protein complex and the mixed-valence species was observed within the first second of reaction. The temperature-dependent properties of the new radical suggest that it may be associated with an iron center and may be a tryptophan-centered radical in the \rm Fe\sp{2+}/Fe\sp{3+}/apoprotein system

Metal Amidoboranes and Their Derivatives for Hydrogen Storage

As potential hydrogen storage mediums, ammonia borane and its derivatives have been paid an increasing attention owing to their higher hydrogen capacities and facile dehydrogenation properties under moderate conditions. In this chapter, we presented extensive studies on thermodynamic tailoring of dehydrogenation of metal amidoboranes, metal borohydride-ammonia borane complexes, and metal amidoborane ammoniates as well as their derivatives, with special focus on the syntheses, crystal structures, and dehydrogenation properties. Finally, future perspective was given toward the practical applications

Distinct composition and amplification dynamics of transposable elements in sacred lotus (Nelumbo nucifera Gaertn.)

Sacred lotus (Nelumbo nucifera Gaertn.) is a basal eudicot plant with a unique lifestyle, physiological features, and evolutionary characteristics. Here we report the unique profile of transposable elements (TEs) in the genome, using a manually curated repeat library. TEs account for 59% of the genome, and hAT (Ac/Ds) elements alone represent 8%, more than in any other known plant genome. About 18% of the lotus genome is comprised of Copia LTR retrotransposons, and over 25% of them are associated with non-canonical termini (non-TGCA). Such high abundance of non-canonical LTR retrotransposons has not been reported for any other organism. TEs are very abundant in genic regions, with retrotransposons enriched in introns and DNA transposons primarily in flanking regions of genes. The recent insertion of TEs in introns has led to significant intron size expansion, with a total of 200 Mb in the 28 455 genes. This is accompanied by declining TE activity in intergenic regions, suggesting distinct control efficacy of TE amplification in different genomic compartments. Despite the prevalence of TEs in genic regions, some genes are associated with fewer TEs, such as those involved in fruit ripening and stress responses. Other genes are enriched with TEs, and genes in epigenetic pathways are the most associated with TEs in introns, indicating a dynamic interaction between TEs and the host surveillance machinery. The dramatic differential abundance of TEs with genes involved in different biological processes as well as the variation of target preference of different TEs suggests the composition and activity of TEs influence the path of evolution

In vitro regeneration of ‘Feizixiao’ litchi (Litchi chinensis Sonn.)

A simple efficient in vitro plant regeneration system was developed by indirect somatic embryogenesis of ‘Feizixiao’ litchi (Litchi chinensis Sonn.). Pollen in the anther of monocytes was used to induce callus. Two auxins (naphthalene acetic acid [NAA] and 2,4-dichloriphenoxyacetic acid [2,4-D]), and two cytokines (kinetin [KT] and 6-benzyladenine [BA]) were tested to explore their influence on callus induction. MS medium supplemented with 2.22 μM BA, 2.69 μM NAA, 13.57 μM 2,4-D, and 0.4 g/L LH (lactalbumin hydrolysate) showed the highest callus induction frequency. The callus obtained from anther was subcultured in MS medium containing 4.52 μM 2,4-D to obtain synchronized friable embryogenic callus. Different developmental stages of SEs were obtained from the callus on MS medium containing 6% (w/v) sucrose and different PGRs (plant growth regulators). On MS medium containing 6% (w/v) sucrose and supplemented with 0.54 μM NAA, 23.23 μM KT, 0.4 g/L LH, 0.56 μM inositol, and 10% (w/v) CW (coconut water), a higher number of SEs (globular, heart, torpedo and cotyledonary embryos) was achieved than on other media. Plantlets were established onto half-strength MS medium containing 1.44 μM GA3 (gibberellic acid) followed by successful acclimatization in the greenhouse. With flow cytometry and chromosome counting, ploidy analysis of regenerated plants revealed that the regenerated plantlets were all diploid. This study is the first report on somatic embryogenesis of ‘Feizixiao litchi’, providing an opportunity to improve the cultivar by biotechnology methods.Keywords: litchi (Litchi chinensis Sonn.), anther culture, callus, regeneration, somatic embryogenesi

A Pseudo DNA Cryptography Method

The DNA cryptography is a new and very promising direction in cryptography research. DNA can be used in cryptography for storing and transmitting the information, as well as for computation. Although in its primitive stage, DNA cryptography is shown to be very effective. Currently, several DNA computing algorithms are proposed for quite some cryptography, cryptanalysis and steganography problems, and they are very powerful in these areas. However, the use of the DNA as a means of cryptography has high tech lab requirements and computational limitations, as well as the labor intensive extrapolation means so far. These make the efficient use of DNA cryptography difficult in the security world now. Therefore, more theoretical analysis should be performed before its real applications. In this project, We do not intended to utilize real DNA to perform the cryptography process; rather, We will introduce a new cryptography method based on central dogma of molecular biology. Since this method simulates some critical processes in central dogma, it is a pseudo DNA cryptography method. The theoretical analysis and experiments show this method to be efficient in computation, storage and transmission; and it is very powerful against certain attacks. Thus, this method can be of many uses in cryptography, such as an enhancement insecurity and speed to the other cryptography methods. There are also extensions and variations to this method, which have enhanced security, effectiveness and applicability.Comment: A small work that quite some people asked abou