The mechanism in the asymmetrically selective oxidation of 3.4-dihydroxyphenylalanine catalyzed by the poly-L-lysine-copper(II) complex

In the oxidation of 3.4-dihydroxyphenylalanine (DOPA) the effect of the asymmetrical structure in poly-L -lysine-copper(II) complex (PLL-Cu(II)) on the asymmetrical selectivity ratio was investigated at various reaction temperatures and various preparation conditions of the catalyst, or by addition of catechol or phenylalanine. From the comparison of the asymmetric selectivity with the structure of the catalyst, the combination of two or more asymmetric cupric complex units was considered as the cause for the asymmetrically selective catalysis, where α-helical structure may serve to hold the two or more cupric complex units in a special steric configuration. Moreover a plausible mechanism for the asymmetrically selective oxidation was discussed by the evidence from the addition effects of catechol or phenylalanine and by the asymmetrically selective interaction between PLL-Cu(II) and DOPA. Then, the mechanism seems to be confirmed by an inspection with a molecular model.     

Induced circular dichroism of biphenyl and its derivatives in mesophase

The mesophase induced circular dichroism (CD) of biphenyl and its derivatives was investigated using the Tween 80 (monooleate of the ether of sorbitan with 4 mol of polyethyleneglycol)-water system, which can form a twisted smectic mesophase. The sign of CD bands in this mesophase is explained by a modified C₂-symmetry rule, since it can be considered that alignment of the solute molecules in this mesophase can be elucidated in terms of a pseudo-C₂ symmetry, when the concentration of the solute is comparatively high. The assignments of the electronic transitions of the solute molecules show a good accordance with results of magnetic circular dichroism study.     

The molecular weight dependence on the photoconductivity of poly(N-vinylcarbazole)

Poly(N-vinylcarbazole), (PNVC), was prepared, fractionated by gel permeation chromatography, and then characterized by viscometry and vapour pressure osmometry. The fractionated PNVC species with relatively narrow molecular weight distributions were successfully used to measure both their electrical dark-conductivity and photoconductivity using a surface type cell in high vacuum (ca. 10^?7 mm Hg) at room temperature. A molecular weight dependent photoconductivity was found for the fractionated PNVCs with weight average molecular weights in the range of 1,2·10³ to 2,4·10⁵. This observation is in contradiction to Epping's results who has found a molecular weight independent photoconductivity in the molecular weight range of 3·10⁵ to 7·10⁶. Our molecular weight dependence may be well understood in terms of the interrupted overlap of the π-electrons of adjacent carbazolyl groups at the terminal parts of the polymer chains, this effect being all the more stronger the smaller the molecular weight is.     

Effect of maximal arm exercise on skin blood flux in the paralyzed lower limbs in persons with spinal cord injury

 The purpose of the present study was to examine the effect of maximal arm exercise on the skin blood circulation of the paralyzed lower limbs in persons with spinal cord injury (PSCI). Eight male PSCI with complete lesions located between T3 and L1 performed graded maximal arm-cranking exercise (MACE) to exhaustion. The skin blood flux at the thigh (SBFT) and that at the calf (SBFC) were monitored using laser-Doppler flowmeter at rest and for 15 s immediately after the MACE. The subject's mean peak oxygen uptake and peak heart rate was 1.41 ± 0.22 l · min^–1 and 171.6 ± 19.2 beats · min^–1, respectively. No PSCI showed any increase in either SBFT or SBFC after the MACE, when compared with the values at rest. These results suggest that the blood circulation of the skin in the paralyzed lower limbs in PSCI is unaffected by the MACE. Accepted: 12 September 1996     

Crystal Growth in Poly(L‐lactide) Thin Film Revealed by in situ Atomic Force Microscopy

Direct visualization of crystal growth in poly(L ‐lactide) thin films was carried out by using a temperature‐controlled atomic force microscopy (AFM). At the initial stage of crystallization, edge‐on lamellar crystals have nucleated and elongated. Subsequently, the edge‐on lamellar crystals showed S‐shaped morphology and changed their orientation from edge‐on manner to flat‐on one. The curvature of edge‐on lamellar crystal has been discussed in terms of inclination and distortion of polymer chains in the crystal. In addition, mechanism on the formation of flat‐on crystal from edge‐on lamellae was proposed as derivative growth on the basis of in situ AFM observation of crystal growth and enzymatic degradation.

     

Genetic alterations of phosphoinositide 3-kinase subunit genes in human glioblastomas

Genetic alterations of PI3K (phosphoinositide 3-kinase) subunits have been documented in a number of tumor types, with increased PI3K activity linked to gene amplification and mutation of catalytic subunits, as well as mutations of regulatory subunits. Among high grade gliomas, activation of the PI3K-AKT signaling pathway through loss of PTEN function is common. We therefore investigated whether genetic alteration of class IA PI3Ks might provide a mechanism for deregulation of this pathway in glioblastomas. We studied a series of glioblastomas with FISH to assess copy number of catalytic subunits (PIK3CA and PIK3CD) and with PCR-SSCP to screen for somatic mutations of conserved regions of both catalytic and regulatory subunits. FISH revealed frequent balanced copy number increases of both PIK3CA and PIK3CD, and one case showed an extra copy limited to PIK3CA. One glioblastoma exhibited a 9-bp deletion that encompassed the exon-intron junction of exon 12 of PIK3R1, documenting for the first time a mutation within a PI3K regulatory subunit in human glioblastoma. This deletion would be predicted to yield a truncated protein that lacks the inhibitory domain, resulting in increased PI3K activity. Furthermore, the case with selected PIK3CA copy number gain and the case with a truncating PIK3R1 mutation both featured AKT activation without PTEN mutation. These results suggest that genetic alterations of class IA PI3K subunit genes can occasionally play a role in human glioblastoma by activating the PI3K-AKT signaling pathway independently of PTEN mutation.     

REACTIVITY OF LYMPHOCYTE SUBPOPULATIONS IN HUMAN MIXED LYMPHOCYTE CULTURE

Loss of antigenicity in the mixed lymphocyte culture (MLC) reaction of lymphocytes precultured at 22°C for 7–10 days was accompanied by a decrease in bone-marrow-derived lymphocytes (B cells) from 22 ± 1% to 13 ± 1%, and an increase in thymus-derived lymphocytes (T cells) from 65 ± 2% to 83 ± 1% (P < 0.001). Depletion of B cells from a fresh lymphocyte suspension by either antihuman immunoglobulin-coated column fractionation or by sheep red blood cell (SRBC) rosette formation resulted in a significant reduction of the cell's ability to stimulate in MLC (P < 0.001). Coating of lymphocytes with rabbit antihuman brain serum abrogated their ability to respond but not the ability to stimulate in MLC.