No abstract

Tyrosinase catalyzes the rate‐limiting step in melanin synthesis. Melanin is synthesized from l‐tyrosin in the melanosomes, where tyrosinase and other melanogenic factors are recruited via the vesicle transport system. Genetic and biochemical approaches have revealed a correlation between impairments in the vesicle transport system and albinism. However, the specificity of the individual transport systems for the corresponding melanogenic factors has not been well elucidated yet. Here, we report that the thioxothiazolidin derivative, 4‐OST (4‐[(5E)‐5‐[(4‐fluorophenyl)methylidene]‐4‐oxo‐2‐sulfanylidene‐1,3‐thiazolidin‐3‐yl]‐4‐azatricyclo [5.2.1.02,6]dec‐8‐ene‐3,5‐dione: CAS RN. 477766‐87‐3) strongly inhibited melanogenesis in mouse melanoma B16F10 cells. 4‐OST reduces tyrosinase protein levels without affecting its messenger RNA levels or enzymatic activity. Although a reduction in tyrosinase protein level was observed in the presence of a protein synthesis inhibitor, the reduction may be coupled with protein synthesis. Similarly, GIF‐2202 (a derivative of 4‐OST) lowers tyrosinase protein levels without affecting the levels of another melanogenic enzyme, tyrosinase‐related protein 1 (TYRP1) level. The reduction in tyrosinase protein level is associated with an increase in the levels of the lysosomal proteinase cathepsin S. Chloroquine, a lysosome inhibitor, restored the tyrosinase protein level downregulated by GIF‐2202, although no effects of other inhibitors (against proteasome, autophagy, or exocytosis) were observed. In addition, GIF‐2202 segregated the immunofluorescence signals of tyrosinase from those of TYRP1. Chloroquine treatment resulted in co‐localization of tyrosinase and cathepsin S signals near the perinuclear region, suggesting that 4‐OST and GIF‐2202 may alter the destination of the tyrosinase vesicle from the melanosome to the lysosome. 4‐OST and GIF‐2202 can be new tools for studying the tyrosinase‐specific vesicle transport system.

It has been reported that the experimental investigations on the synchronization probabilities of the two surface streamers in atmospheric air by the authors. This synchronization phenomenon is interpreted by following processes. When an impulse voltage is applied to the parallel connected electrodes, a prior streamer occurs and the propagating streamer emits light. This light passes through the air and reaches the other electrode area. In this area, the initial electrons are supplied by the light and the initial electrons trigger the second streamer. The wavelength region of the light effective for the synchronization was confirmed experimentally. The region was shorter than 250 nm but the detailed wavelength cannot be specified by the experiments. Accordingly, as the first step to specify the effective wavelength, VUV emission spectra from DC positive corona discharges in air are observed together with nitrogen and oxygen gases. Several strong line spectra emitted from the discharges in air are recognized. They are identified that the emission lines of 174 nm, 149 nm and 118 nm are radiated from atomic nitrogen. On the other hand, the emission lines of 120 nm and 130 nm are originated from atomic oxygen. The preliminary experimental results show that these lights are absorbed immediately in air, so on-site photoabsorption measurements were carried out in air. The absorption coefficients of the air are estimated in this study. Even if the wavelength of the light is in the region of VUV, the light can pass through in the air. The facts suggest that the VUV light can pass through long distance in air and the light is effective for the propagation and the synchronization of streamer discharges through the photoelectron emission.