Elucidation of the Tetraterpene Hydrocarbon Biosynthetic Pathway in the Green Microalga Botryococcus braunii Race L

The colony-forming green microalga Botryococcus braunii is a potential source of biofuel feedstocks as it produces large amount of liquid hydrocarbon oils that can be converted into combustion engine fuels. There are three different races of B. braunii based on the hydrocarbons it synthesizes. Race A produces fatty acid derived alkadienes and alkatrienes, race B produces the triterpenoid The colony-forming green microalga Botryococcus braunii is a potential source of biofuel feedstocks as it produces large amount of liquid hydrocarbon oils that can be converted into combustion engine fuels. There are three different races of B. braunii based on the hydrocarbons it synthesizes. Race A produces fatty acid derived alkadienes and alkatrienes, race B produces the triterpenoid hydrocarbons tetramethylsqualene and botryococcenes, and race L, the focus of this study, produces the C₄₀ tetraterpenoid hydrocarbon lycopadiene via a previously uncharacterized biosynthetic pathway. Structural similarities suggest this pathway follows a biosynthetic mechanism analogous to that of C₃₀ squalene. Confirming this hypothesis, the studies presented here identified C₂₀ geranylgeranyl diphosphate (GGPP) as a precursor for lycopaoctaene biosynthesis, the first committed intermediate in the production of lycopadiene. Two squalene synthase (SS)-like cDNAs were identified in race L with one encoding a true SS, and the other an enzyme with lycopaoctaene synthase (LOS) activity. Interestingly, LOS utilizes alternative C₁₅ and C₂₀ prenyl diphosphate substrates to produce combinatorial hybrid hydrocarbons, but almost exclusively utilizes GGPP in vivo. This discovery highlights how SS enzyme diversification resulted in the production of specialized tetraterpenoid oils in race L of B. braunii. To understand LOS substrate and product specificity, rational mutagenesis experiments were conducted based on sequence alignments with several SS proteins as well as a structural comparison with the human SS (HSS) crystal structure. Characterization of the LOS mutants in vitro identified Ser276 and Ala288 in the LOS active site as key amino acids responsible for controlling substrate binding, and thus the promiscuity of this enzyme. Mutating these residues to those found in HSS largely converted LOS from lycopaoctaene production to C₃₀ squalene production. Furthermore, these studies were confirmed in vivo by expressing LOS in E. coli cells metabolically engineered to produce high FPP and GGPP levels. These studies also offer insights into tetraterpenoid hydrocarbon metabolism in B. braunii and provide a foundation for engineering LOS for robust production of specific hydrocarbons of a desired chain length

New record of earthworm Eukerria kuekenthali (Oligochaeta: Ocnerodrilidae) from Sikkim, India

The earthworm genus Eukerria kuekenthali (Michaelsen 1908) is recorded for the first time from the Sikkimese soil. Inter/ intra specific variations have not been observed. Altitude plays a vital role in the distribution pattern of this species. The photographic descriptions with illustrations are provided

Ergonomy in laboratory animal care

No abstract availabl

Investigation of Co2_2FeSi: The Heusler compound with Highest Curie Temperature and Magnetic Moment

This work reports on structural and magnetic investigations of the Heusler compound Co$_2$FeSi. X-Ray diffraction and M\"o\ss bauer spectrometry indicate an ordered $L2_1$ structure. Magnetic measurements by means of X-ray magnetic circular dichroism and magnetometry revealed that this compound is, currently, the material with the highest magnetic moment ($6 \mu_B$) and Curie-temperature (1100K) in the classes of Heusler compounds as well as half-metallic ferromagnets

Elucidation of the Tetraterpene Hydrocarbon Biosynthetic Pathway in the Green Microalga Botryococcus braunii Race L

The colony-forming green microalga Botryococcus braunii is a potential source of biofuel feedstocks as it produces large amount of liquid hydrocarbon oils that can be converted into combustion engine fuels. There are three different races of B. braunii based on the hydrocarbons it synthesizes. Race A produces fatty acid derived alkadienes and alkatrienes, race B produces the triterpenoid The colony-forming green microalga Botryococcus braunii is a potential source of biofuel feedstocks as it produces large amount of liquid hydrocarbon oils that can be converted into combustion engine fuels. There are three different races of B. braunii based on the hydrocarbons it synthesizes. Race A produces fatty acid derived alkadienes and alkatrienes, race B produces the triterpenoid hydrocarbons tetramethylsqualene and botryococcenes, and race L, the focus of this study, produces the C₄₀ tetraterpenoid hydrocarbon lycopadiene via a previously uncharacterized biosynthetic pathway. Structural similarities suggest this pathway follows a biosynthetic mechanism analogous to that of C₃₀ squalene. Confirming this hypothesis, the studies presented here identified C₂₀ geranylgeranyl diphosphate (GGPP) as a precursor for lycopaoctaene biosynthesis, the first committed intermediate in the production of lycopadiene. Two squalene synthase (SS)-like cDNAs were identified in race L with one encoding a true SS, and the other an enzyme with lycopaoctaene synthase (LOS) activity. Interestingly, LOS utilizes alternative C₁₅ and C₂₀ prenyl diphosphate substrates to produce combinatorial hybrid hydrocarbons, but almost exclusively utilizes GGPP in vivo. This discovery highlights how SS enzyme diversification resulted in the production of specialized tetraterpenoid oils in race L of B. braunii. To understand LOS substrate and product specificity, rational mutagenesis experiments were conducted based on sequence alignments with several SS proteins as well as a structural comparison with the human SS (HSS) crystal structure. Characterization of the LOS mutants in vitro identified Ser276 and Ala288 in the LOS active site as key amino acids responsible for controlling substrate binding, and thus the promiscuity of this enzyme. Mutating these residues to those found in HSS largely converted LOS from lycopaoctaene production to C₃₀ squalene production. Furthermore, these studies were confirmed in vivo by expressing LOS in E. coli cells metabolically engineered to produce high FPP and GGPP levels. These studies also offer insights into tetraterpenoid hydrocarbon metabolism in B. braunii and provide a foundation for engineering LOS for robust production of specific hydrocarbons of a desired chain length

Hyperinsulinism in short-chain L-3-hydroxyacyl-CoA dehydrogenase deficiency reveals the importance of beta-oxidation in insulin secretion

A female infant of nonconsanguineous Indian parents presented at 4 months with a hypoglycemic convulsion. Further episodes of hypoketotic hypoglycemia were associated with inappropriately elevated plasma insulin concentrations. However, unlike other children with hyperinsulinism, this patient had a persistently elevated blood spot hydroxybutyrylcarnitine concentration when fed, as well as when fasted. Measurement of the activity of L-3-hydroxyacyl-CoA dehydrogenase in cultured skin fibroblasts with acetoacetyl-CoA substrate showed reduced activity. In fibroblast mitochondria, the activity was less than 5% that of controls. Sequencing of the short-chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD) genomic DNA from the fibroblasts showed a homozygous mutation (C773T) changing proline to leucine at amino acid 258. Analysis of blood from the parents showed they were heterozygous for this mutation. Western blot studies showed undetectable levels of immunoreactive SCHAD protein in the child's fibroblasts. Expression studies showed that the P258L enzyme had no catalytic activity. We conclude that C773T is a disease-causing SCHAD mutation. This is the first defect in fatty acid beta -oxidation that has been associated with hyperinsulinism and raises interesting questions about the ways in which changes in fatty acid and ketone body metabolism modulate insulin secretion by the beta cell. The patient's hyperinsulinism was easily controlled with diazoxide and chlorothiazide

Covalent bonding and the nature of band gaps in some half-Heusler compounds

Half-Heusler compounds \textit{XYZ}, also called semi-Heusler compounds, crystallize in the MgAgAs structure, in the space group $F\bar43m$. We report a systematic examination of band gaps and the nature (covalent or ionic) of bonding in semiconducting 8- and 18- electron half-Heusler compounds through first-principles density functional calculations. We find the most appropriate description of these compounds from the viewpoint of electronic structures is one of a \textit{YZ} zinc blende lattice stuffed by the \textit{X} ion. Simple valence rules are obeyed for bonding in the 8-electron compound. For example, LiMgN can be written Li$^+$ + (MgN)$^-$, and (MgN)$^-$, which is isoelectronic with (SiSi), forms a zinc blende lattice. The 18-electron compounds can similarly be considered as obeying valence rules. A semiconductor such as TiCoSb can be written Ti$^{4+}$ + (CoSb)$^{4-}$; the latter unit is isoelectronic and isostructural with zinc-blende GaSb. For both the 8- and 18-electron compounds, when \textit{X} is fixed as some electropositive cation, the computed band gap varies approximately as the difference in Pauling electronegativities of \textit{Y} and \textit{Z}. What is particularly exciting is that this simple idea of a covalently bonded \textit{YZ} lattice can also be extended to the very important \textit{magnetic} half-Heusler phases; we describe these as valence compounds \textit{ie.} possessing a band gap at the Fermi energy albeit only in one spin direction. The \textit{local} moment in these magnetic compounds resides on the \textit{X} site.Comment: 18 pages and 14 figures (many in color

Spatio-temporal dynamics of anisotropic emission from nano second laser produced aluminium plasma

Polarized emission carries captivating information and can help understand various elementary processes involving collisions within the plasma as well as in radiative transitions. In this work, we investigate the spatio-temporal dependence of the emission anisotropy of a nanosecond laser produced aluminium plasma at 100 mbar background pressure. We observe that the anisotropy of the emission spectra exhibits interesting spatio-temporal characteristics which in turn depend on the charge state of the emitting species. The degree of polarization (DOP) is found to reverse its sign along the plume propagation direction. Observed behaviour in DOP appears to be due to the contribution from various involved atomic processes. However, closer to the sample the contribution from the self-generated magnetic field predominantly affect the polarization. On the other hand, the effect of the self generated magnetic field on the observed polarized emission is insignificant as the plume propagates away from the sample. This is of particular interest in polarization resolved laser induced breakdown spectroscopy as spatio-temporal profile of the degree of polarization has to be properly taken into account prior to the spectral analysis