Natural,semisynthetic and synthetic tyrosinase inhibitors

Tyrosinase plays a pivotal role in the synthesis of melanin pigment synthesis on skin utilizing tyrosine as a substrate. Melanin is responsible for the protection against harmful ultraviolet irradiation, which can cause significant pathological conditions, such as skin cancers. However, it can also create esthetic problems when accumulated as hyperpigmented spots. Various skin-whitening ingredients which inhibit tyrosinase activity have been identified. Some of them, especially ones with natural product origins, possess phenolic moiety and have been employed in cosmetic products. Semi-synthetic and synthetic inhibitors have also been developed under inspiration of the natural inhibitors yet some of which have no phenolic groups. In this review, tyrosinase inhibitors with natural, semi-synthetic and synthetic origins are listed up with their structures, activities and characteristics. Further, a recent report on the adverse effect of a natural melanin synthesis inhibitor which was included in skin-whitening cosmetics is also briefly discussed.     

Elementary steps in the formation of horseradish peroxidase compound I: direct observation of compound 0, a new intermediate with a hyperporphyrin spectrum

The reaction of horseradish peroxidase (HRP) with H2O2 has been studied in 50% v/v methanol/water over the 25.0 to -36.0 degrees C temperature range by using the low-temperature stopped-flow technique. All reactions were carried out under pseudo-first-order conditions with [H2O2] much greater than [HRP]. Arrhenius plots for the pseudo-first-order rate constant kobs were linear over the 17.6 to -36.0 degrees C temperature range studied with an activation energy of 4.8 +/- 0.5 kcal/mol. Above 0 degrees C, kobs varies linearly with peroxide concentration. However, saturation kinetics are observed below -16.0 degrees C, indicating that there is at least one reversible elementary step in this reaction. Double-reciprocal plots at -26.0 degrees C at pH* 7.3 for the reaction give kappa max(obs) = 163 s-1 and KM = 0.190 mM. Rapid-scan optical studies carried out at -35.0 degrees C with [H2O2] much greater than KM reveal the presence of a transient intermediate referred to as compound 0 whose conversion to compound I is rate limiting. The Soret region of the optical spectrum of compound 0 resembles that of a "hyperporphyrin" with prominent bands near 330 and 410 nm. The temperature dependencies of kappa max(obs) and KM have been measured over the -16.0 to -26.0 degrees C range and give an activation energy for kappa max(obs) of 1.6 +/- 0.7 kcal/mol and an enthalpy of formation for compound 0 of 4.0 +/- 0.7 kcal/mol.     

Ecology of deepwater rice-fields in Bangladesh 4. Nitrogen fixation by blue-green algal communities

1. Aquatic macrophytes formed dense beds in fallow areas during the four and a half months of the flood season in all but one deepwater rice-growing location in Bangladesh; these included several types of life-form, but the fine-leaved species, Myriophyllum sp., Najas indica, Utricularia stellaris were often especially abundant. The same species grew inside deepwater rice fields, but at much lower densities. A similar contrast occurred for the algae, although deepwater rice often developed dense masses of epiphytes on aquatic roots, stems and leaf sheaths, when plants were growing in isolated, well-illuminated situations.
2. Two widespread algae, Aulosira fertilissima and Scytonema mirabile, were equally successful on soil in the period prior to the arrival of floodwaters and floating on the surface of the water during the flood season. Other species common during the flood season differed from those common on soil.
3. Most blue-green algae inside deepwater rice fields were heterocystous; the only species not so, but forming distinct colonies, was Aphanothece stagnina. However only non-heterocystous forms were found at one location in south Bangladesh (Phaltita) and a change from heterocystous to non-heterocystous forms was noted at the main research site (near Sonargaon) during late September in at least one year. The water column at the former was almost entirely anoxic, while the change at the latter occurred at a time when the water sometimes became anoxic during the night. It is suggested that differences in ability to tolerate anoxic periods may be a key factor in determining the success of the algal and vascular plant species in the different micro-habitats within these DWR-growing areas.
4. Although diatoms were quantitatively only a minor component of the algal biomass, they became more frequent later in the season when the water became microaerobic or anoxic for part of the day. Navicula confervacea was overall the most abundant species at the two main research locations.

     

Chromosome aberrations in workers of nuclear-power plants

The frequencies of chromosome aberrations in 135 workers from nuclear-power plants were compared with those in 135 age-matched controls. A total of 135,000 cells was scored. The frequencies of dicentric chromosome were 1.67 × 10⁻³ in the exposed group and 0.49 × 10⁻³ in the control group and those of chromosome-type deletion were 3.33 × 10⁻³ and 1.10 × 10⁻³, respectively. The frequencies of all types of chromosome aberrations in the exposed subjects were higher than those in the control group, but no significant trend of dose-dependent increase was observed when only the exposed group were considered. Poisson regression analysis, with both exposed and control included, showed that there was a significant association of chromosome aberration with radiation dose and the duration of work, but not with age, smoking habit and alcohol intake. It was also found that recent exposure to radiation, within the last 5 years, had contributed more to the observed chromosome aberration than earlier exposure.     

Genetic and clonal diversity in Korean populations ofVitex rotundifolia (Verbenaceae)

Vitex rotundifolia L.f. is a woody perennial and has sexual and asexual modes of reproduction. Allozyme study was conducted on 550 plants in 13 Korean populations. The levels of genetic variability and divergence within and among populations, respectively, are considerably lower and higher than the mean values for woody plants with similar life history tralts. Mean percentage of polymorphic loci (P _P), mean number of alleles per locus (A _P), and mean genetic diversity (He _P) within populations ofV. rotundifolia were: 16.7%, 1.21, and 0.047. On average, about 79% of the total variation inV. rotundifolia was common to all populations (meanG _ST=0.208). In addition, significant differences in allele frequencies among populations were found in all polymorphic loci examined (P<0.001). On the other hand, levels of genotypic diversity within and among populations were moderate. About 44% (18/41) of multilocus genotypes were “local genotypes” (genotypes occurring in only one population), whereas only one “widespread genotype” (genotypes occurring in more than 75% of the populations) were detected. The mean number of multilocus genotypes per population (G) and mean genotypic diversity index (D _G) were 8.4 and 0.74, respectively. Most common multilocus genotypes found in populations were homozygous for five polymorphic loci. The abundance of ramets of these genets is responsible for the low levels of expected heterozygosity within populations. The results indicate that clonal reproduction may act as an enhancer of genetic drift by reducing effective size of local populations ofV. rotundifolia.     

Expression of the Lactobacillus casei lactate dehydrogenase gene in Bacillus subtilis

Summary A gene for allosteric lactate dehydrogenase (LDH) of Lactobacillus casei ATCC393 was transferred into Bacillus subtilis. The LDH was produced in a growth-associated type, and comprised up to 40 % of the total cellular protein. The maximum specific activity in the transformant was 208 U/mg protein which was approximately 16 times higher than in L. casei or in the previously constructed Escherichia coli transformant.     

Noncytotoxic Dy3+-activated glass emits cool white light for near ultraviolet-based white light-emitting diodes,visible lasers,and biomedical applications

Using the melt quenching technique, a lithium zinc borate glass (LZB) system with trivalent dysprosium ions (Dy³⁺) was synthesized, and the luminescence and lasing properties of these materials were examined for the generation of white light. Structural investigation through X-ray diffraction revealed that the prepared glass had an amorphous nature. The optimized glass containing 0.5 Dy³⁺ had a direct optical band gap of 2.782 eV and an indirect optical band gap of 3.110 eV. A strong excitation band at 386 nm (⁶H_15/2→⁴I_13/2) was recognized in the ultraviolet (UV) light region of its excitation spectrum. Emission bands could be seen in the photoluminescence spectrum at 659, 573, and 480 nm under the 386 nm excitation. These transitions of emission resembled electronic transitions such as (⁴F_9/2→⁶H_11/2), (⁴F_9/2→⁶H_13/2), and (⁴F_9/2→⁶H_15/2). In a pristine glass matrix, the higher intensity ratio of yellow to blue can result in the production of white light. The optimized Dy³⁺ ion concentration was observed to be 0.5 mol%. In addition, an analysis of lifetime decay was conducted for all synthesized glasses, and their decay trends were systematically investigated. Noticeably, we assessed the photometric parameters and found that they were close to the white light standard. Furthermore, a cytotoxicity study was carried out using lung fibroblast (WI-38) cell lines for the optimized 0.5Dy³⁺-doped LZB glass and it appeared to be noncytotoxic. It is clear from the results that the noncytotoxic LZB glass doped with 0.5 Dy³⁺ ions could be a suggestive choice for the manufacture of white light-emitting diodes and lasers using near-UVs.