The crystal structure of adenylosuccinate synthetase from Escherichia coli

The crystal structure of adenylosuccinate synthetase from Eschericha coli has been pursued to a resolution of 3.7 A. Using isomorphous and anomalous (SIRAS) phases from a HgI[subscript]4[superscript]2- derivative, electron density maps were generated that clearly revealed the envelope of the enzyme dimer and the two-fold molecular symmetry of the dimer;Since the enzyme is active as a dimer consisting of two identical monomers, the method of density averaging (Bricogne, 1976) was employed to improve the electron density map based on SIRAS phases. The non-crystallographic two-fold operator, which relates two monomers, was refined against an SIRAS electron density map of 4.0 A resolution. The molecular two-fold axis was found about 10° away from the direction perpendicular to the crystallographic two-fold screw axis, significantly different from its previous location (Serra, 1990);The polypeptide conformation from the N terminus to the C terminus was traced in the averaged electron density map at 3.7 A resolution. Although there were some regions of discontinuous density, particularly at the surface of the enzyme, secondary structures were recognizable. On the basis of the assigned positions of the N and the C terminus and sequence homology to other mononucleotide binding proteins, the tentative binding sites for mononucleotides and succinate were determined;Reference. Bricogne, G. J. Mol. Biol. 1976, A32, 832-847. Serra, M. A. Ph.D. Dissertation, Iowa State University, 1990

Expanding Universe and Dynamical Compactification Using Yang-Mills Instantons

We consider an eight-dimensional Einstein-Yang-Mills theory to explore whether Yang-Mills instantons formed in extra dimensions can induce the dynamical instability of our four-dimensional spacetime. We show that the Yang-Mills instantons in extra dimensions can trigger the expansion of our universe in four-dimensional spacetime as well as the dynamical compactification of extra dimensions. We also discuss a possibility to realize a reheating mechanism via the quantum back-reaction from the contracting tiny internal space with a smeared instanton.Comment: v3; 26 pages, 6 figures, version to be published in JHE

Building the Korean Film Industry\u27s Competitiveness: Abolish the Screen Quota and Subsidize the Film Industry

Under Korean law, local theaters in Korea must show Korean films for at least 146 days each year. In 1998, this screen quota became the subject of heated debate between the United States and the Korean film industry when the United States demanded that Korea abolish it. The United States believes the quota violates free trade principles, while the Korean film industry argues that cultural products such as films cannot be equated with other commercial commodities. Cultural identities must be protected because a diversified global culture benefits all. Domestic film industries should be protected because films constitute a vehicle for transmitting cultural values. One way to promote Korean culture is to encourage the production of films that portray Korean culture and to ensure that these films are commercially viable. Korea\u27s screen quota does not ensure that Korean films will depict Korean culture; instead, it merely requires films made in Korea to be shown in theatres. The screen quota is also problematic because it encourages complacency on the part of the Korean film industry toward domestic and global competitors. Government subsidies tied to film quality and cultural content, on the other hand, would promote Korean culture and ensure that Korean films are commercially viable. In Europe, subsidies have proven to be effective in stimulating domestic film industries to produce quality films that are commercially viable. Through subsidies, the Korean government can ensure that Korean culture will be preserved and promoted through film

Solvable Potentials from Supersymmetric Quantum Mechanics

A recurrence relation of Riccati-type differential equations known in supersymmetric quantum mechanics is investigated to find exactly solvable potentials. Taking some simple {\it ans\"atze}, we find new classes of solvable potentials as well as reproducing the known shape-invariant ones.Comment: 14 pages, Late

Labisia pumila extract protects skin cells from photoaging caused by UVB irradiation

Labisia pumila (Myrsinaceae), known as "Kacip Fatimah," has been used by many generations of Malay women to induce and facilitate child birth as well as a post partum medicine. However, its topical application on skin has not been reported yet. In this study, we have focused on the anti-photoaging effects of L. pumila. Extract of L. pumila was first analyzed for their antioxidant activities using DPPH (2,2-diphenyl-1-picrylhydrazyl) since UV irradiation is a primary cause of reactive oxygen species (ROS) generation in the skin. The 50% free radical scavenging activity (FSC(50)) of L. pumila extract was determined to be 0.006%, which was equal to that produced by 156 microM ascorbic acid. TNF-alpha and cyclooxygenase (COX-2) play a primary role in the inflammation process upon UV irradiation and are known to be stimulated by UVB. Treatment with L. pumila extract markedly inhibited the TNF-alpha production and the expression of COX-2. Decreased collagen synthesis of human fibroblasts by UVB was restored back to normal level after treatment with L. pumila extract. On the other hand, the enhanced MMP-1 expression upon UVB irradiation was down regulated by L. pumila extract in a dose-dependent manner. Furthermore, treatment of normal keratinocytes with L. pumila extract attenuated UVB-induced MMP-9 expression. These results collectively suggest L. pumila extract has tremendous potential as an anti-photoaging cosmetic ingredient