Search

Rh was loaded on various supports including ceria by a colloid deposition method. The average particle size of the starting Rh colloid was about 50 A. When it was deposited on alumina or zinc oxide, Rh particles were clearly observed by a TEM analysis. However, no TEM image of Rh was obtained on ceria which was prepared by calcination at 550°C. ESCA and XRD analyses revealed that Rh penetrated into the ceria and only a small amount remained on the surface. On the other hand Rh was present as metallic particles on the surface of ceria which was calcined at 950°C. The ceria calcined at a low temperature (550°C) had high surface area; thus, this ceria had high surface energy and could dissolve Rh. Although the amount of Rh exposed on the surface of ceria was small, the Rh in this state was highly active in decomposing methanol.

Previously, we reported that ganglioside GQ1b specifically promoted neuritogenesis of human neuroblastoma cells (GOTO), and also that it specifically stimulated the phosphorylation of several cell surface proteins on the same cells. To disclose the relationship between the two events, we examined them using a novel protein kinase inhibitor, K-252b, which is a derivative of K-252a and cannot pass through cell membrane. K-252b inhibited the GQ1b-dependent neuritogenesis as well as the GQ1b-stimulated phosphorylation. This suggests the direct coupling between the two cell events and the occurrence of a new biosignal transduction system.

Exogenously added sialyl cholesterol (SC) induced neuritogenesis and accumulated in the nuclear fraction of a mouse neuroblastoma cell line, Neuro2a, as reported elsewhere. To clarify the significance of nuclear SC, we examined the structure of chromatin and its transcriptional level. The chromatin of SC-treated cells exhibits greater circular dichroism amplitude (260-310 nm) than that of nontreated cells. The transcriptional level of chromatin from SC-treated cells was significantly higher than that of nontreated cells. The chromatin structural change has a good correlation to the transcriptional enhancement. On the addition of SC to the chromatin of nontreated cells, the circular dichroism spectra increased in amplitude and the transcriptional level also increased in a concentration-dependent manner. alpha-Amanitin-treated cells did not show SC-dependent neuritogenesis. These results strongly suggest that nuclear SC affects gene expression, which results in promotion of the neuritogenesis of cells.

Using the shape space of codons and tRNAs we give a physical description of the genetic code evolution on the basis of the codon capture and ambiguous intermediate scenarios in a consistent manner. In the lowest dimensional version of our description, a physical quantity, codon level is introduced. In terms of the codon levels two scenarios are typically classified into two different routes of the evolutional process. In the case of the ambiguous intermediate scenario we perform an evolutional simulation implemented cost selection of amino acids and confirm a rapid transition of the code change. Such rapidness reduces uncomfortableness of the non-unique translation of the code at intermediate state that is the weakness of the scenario. In the case of the codon capture scenario the survival against mutations under the mutational pressure minimizing GC content in genomes is simulated and it is demonstrated that cells which experience only neutral mutations survive.

To determine the mechanisms of the neuritogenesis induced by synthetic sialyl cholesterol (SC) in a mouse neuroblastoma cell line, Neuro2a, the biochemical fate of SC and ganglioside GM1 (IV3NeuAc-GgOse4Cer) was investigated. The kinetics of incorporation of SC and GM1 into cells for the two compounds were similar. SC was not degraded nor modified for at least 24 h after the incorporation, indicating that SC itself and not its metabolites were responsible for the neuritogenic activity. Cell fractionation experiments showed that approximately 40% of the incorporated SC was localized in the nucleus, 25% in the plasma membrane fractions, and 11-14% in the granule fraction. This distribution was different from that of GM1. The nuclear SC was found to affect de novo RNA synthesis, indicating its biological effect may be mediated at the level of transcription. SC also increased the rates of both Ca2+ influx and efflux, although the intracellular level of total Ca2+ remained unchanged. Levels of inositol 1,4,5-triphosphate (IP3) also remained unchanged and the SC dependent neuritogenesis was not inhibited by an excess amount of W-7, an inhibitor of Ca2+/CaM kinases. These results again accord with the suggestion that SC and GM1 do not utilize Ca2+, IP3 or Ca2+/CaM as a second messenger for neuritogenesis. Rather it appears very likely that the nuclear localized SC may play a key role in neuritogenesis.

Amphipathic compounds containing N-acetylneuraminic acid (sialic acid) [for example, D-N-acetylneuraminyl-(alpha 2-1)-2S,3R,4E-2-N-tetracosanoyl sphingenine, sialyl alkyl glycerol ethers, and sialyl cholesterols] induced neuritogenesis in a neuroblastoma cell line (Neuro2a). The sialic acid in the hydrophilic moiety of the compounds is specifically required for neuritogenesis. The requirement for molecular specificity of the hydrophobic moiety, however, is rather low. Regarding the hydrophobic moiety, no preference for cholesterol, alkyl glycerol ether, or ceramide residues was observed as to their neuritogenic activity. Sialyl compounds with alpha-ketosidic sialyl linkages were more active than the corresponding beta-anomers. These sialyl compounds induced the growth of only one neurite, but a long one, from the cell body. This type of neuritogenes is completely different from that induced by compounds capable of elevating the concentration of intracellular cyclic AMP, which induced the appearance of many neurites from a single cell body. Besides this morphological change, the active sialyl compounds also caused a change in the carbohydrate composition of the cell surface. Sialyl compound treatment drastically increased the concentration of peanut agglutinin binding sites.

A ganglioside-stimulated ecto-type protein phosphorylation system (ecto-Gg-kinase) was detected on the cell surface of a human neuroblastoma cell line (GOTO). When intact cells were incubated with [gamma-32P]ATP, at least 28 cell surface proteins were phosphorylated, as evident on SDS-PAGE (4-20%) analysis. Exogenously added gangliosides specifically stimulated the phosphorylation of at least three cell surface associated proteins of Mr = 64,000, 60,000, and 54,000. Phosphorylation was directed toward Thr and Ser residues, respectively, as revealed on acid hydrolysis followed by electrophoresis. GQ1b, at 5 nM, was the most potent among the several gangliosides tested and was more effective when added to cells before [gamma-32P]ATP administration. The simultaneous addition of an excess amount of the saccharide portion of GQ1b (oligo-GQ1b) inhibited the GQ1b-stimulated phosphorylation, indicating the necessity of the sialosaccharide moiety. These results strongly suggest that phosphorylation of the three proteins may be closely associated with the highly specific neuritogenic effect of GQ1b previously reported.