Cytosolic Cysteine Synthase Switch Cysteine and Mimosine Production in <Emphasis Type="Italic">Leucaena leucocephala</Emphasis>

In higher plants, multiple copies of the cysteine synthase gene are present for cysteine biosynthesis. Some of these genes also have the potential to produce various kinds of β-substitute alanine. In the present study, we cloned a 1275-bp cDNA for cytosolic O-acetylserine(thiol)lyase (cysteine synthase) (Cy-OASTL) from Leucaena leucocephala. The purified protein product showed a dual function of cysteine and mimosine synthesis. Kinetics studies showed pH optima of 7.5 and 8.0, while temperature optima of 40 and 35 °C, respectively, for cysteine and mimosine synthesis. The kinetic parameters such as apparent K_m, k_cat were determined for both cysteine and mimosine synthesis with substrates O-acetylserine (OAS) and Na₂S or 3-hydroxy-4-pyridone (3H4P). From the in vitro results with the common substrate OAS, the apparent k_cat for Cys production is over sixfold higher than mimosine synthesis and the apparent K_m is 3.7 times lower, suggesting Cys synthesis is the favored pathway.     

The Effects of Side-Chain Configurations of a Retro–Inverso-Type Inhibitor on the Human T-Cell Leukemia Virus (HTLV)-1 Protease

In this study, the effects of side-chain configurations of D-Ile residues of a retro–inverso (RI)-type inhibitor on the human T-cell leukemia virus type 1 (HTLV-1) protease containing a hydroxyethylamine dipeptide isostere were clarified. Prior to evaluation using the RI-type inhibitor, the effects of side-chain configurations of Ile residues of the substrate peptide on the HTLV-1 protease were examined to estimate the influence of side-chain configurations on enzyme activity. Based on the estimation of the influence of side-chain configurations on protease affinity, the RI-type inhibitors containing a D-allo-Ile residue in the corresponding substrate sequence, instead of a D-Ile residue, were synthesized via 9-fluorenylmethoxycarbonyl-based solid-phase peptide synthesis. Refolded recombinant HTLV-1 protease (1-116, L40I) was used for the simple and short evaluation of the inhibitory activities of the synthesized RI-type inhibitors. The results clearly indicated that mimicking the whole topology, comprising both the main- and side-chain structures of the parent inhibitor, is effective for the design of potent RI-modified protease inhibitors.     

Atomic structure and stability of elliptical carbon onion

Elliptical carbon onions were produced from amorphous carbon by electron beam irradiation. Atomic structure and structural stability of the onion were investigated by high-resolution electron microscopy, molecular mechanics calculation and molecular orbital calculation, and a structure model of C₂₄@ C₈₄ was proposed at the center of the elliptical onion. Received 30 November 2000     

Over-doping of Tl2Ba2CuO6 due to charge transfer Tl-(Cu-O)

Superconductivity was observed in La substituted Tl₂Ba₂CuO₆. Both T_c and unit cell dimension, a, increase with increasing La concentration, indicating that an over-doping state in Tl₂Ba₂CuO₆, which was due to charge transfer Tl^3−t-(Cu-O)^p as supported from XPS measurements, was relieved by La substitution for Ba.     

X-ray photoelectron spectroscopy of Co3O4, Fe3O4, Mn3O4, and related compounds

The metal 2p region spectra of the mixed valence spinels, Co₃O₄, Fe₃O₄, Mn₃O₄, and related compounds were studied. The satellite splittings of Co 2p_{$\text{3}\text{2}$} for the octahedrally coordinated cobaltous ions are 6.2 eV and those for the tetrahedrally coordinated ones are about 5.3 eV. The Co 2p spectrum for Co₃O₄ is considered to be the sum of spectra of magnetic cobaltous ions and low-spin cobaltic ions. In the cases of Fe₃O₄ and Mn₃O₄, the oxidation states were not clearly distinguished because both the divalent and trivalent ions of iron and manganese are high-spin.     

The effect of the next nearest neighbor ion on the X-ray photoelectron spectra of 2p levels for Co2+, Ni2+ and Cu2+ in MgO

The X-ray photoelectron spectra of Co, Ni and Cu 2p levels for samples of M_xMg_1-xO (M = Co, Ni, Cu), CoO, NiO and CuO were compared. The binding energies of metal 2p_{$\text{3}\text{2}$} levels did not change with their concentration. The shake-up satellite main peak intensity ratios and FWHM of metal 2p levels for Co²⁺ and Cu²⁺ in MgO were smaller than those for CoO and CuO. The Ni 2p_{$\text{3}\text{2}$} spectrum for Ni²⁺ in MgO had no shoulder, unlike NiO. Results indicate that next nearest neighbor ions (metal ions) may influence the final states after photoelectron ejection.     

Tetrahydroquinolizinium ylides: preparation and 1,3-dipolar cycloaddition

By the Cu(II)-catalyzed reaction of 2-(4-diazo-3-oxoalkyl)pyridines (2), 4-alkoxycarbonyl (or 4-acyl)-3-oxo-1,2,3,4-tetrahydroquinolizinium ylides (3) were obtained in high yields. From the cycloaddition reaction of 3 with acetylenic esters (propynoates or acetylenedicarboxylates) the labile [2 + 3] cycloadducts, 3-oxo-3H-2a,4,5,8a-tetrahydropyrrolo[2,1,5-de]quinolizine-2a-carboxylates (8 or 12), were identified, which further reacted with DMAD (dimethyl acetylenedicarboxylate) to afford azocine derivatives (15 or 16) and produced pyrrolodihydroquinolizines (9 or 20) by dealkoxycarbonylation.     

Analytical applications of ESCA to samples in powder form

Analytical applications of ESCA to samples in powder form are described. These include the estimation of atomic ratios of metallic elements to oxygen in some typical oxides, the construction of calibration curves and the investigation of precipitation phenomena. The calibration curve method is useful in combination with the calculation method when the appropriate sample preparation has been carried out.