RESUMEN
Large substituent effects were observed in the rates and reaction mechanisms of the photochemical rearrangement of N-arylaza-[60]fulleroid 1 to N-arylaziridino-[60]fullerene 2, in which the difference of the rates between the fastest and the slowest (>2160-fold) was attained only by changing the aryl group from 1-naphthyl to 2-naphthyl. The decreasing order of the reaction rates in relation to the substituents was 1-naphthyl (1b) > 1-pyrenyl (1d) > phenyl (1a) > 2-naphthyl (1c). The reactions proceeded via triplet states of the fulleroids and a triplet sensitization of the reaction by rearranged product 2b was observed in the case of 1b. The slow reactions of 1a,c were interpretated by the participation of charge-separated species in the excited triplet states, which was supported by nanosecond transient absorption spectra.
RESUMEN
Here, we show that fibronectin (FN) peptides derived from two distinct regions promote the insulin-induced adipocyte differentiation of ST-13 cells by preventing FN fibrillogenesis. ST-13 cells formed numerous FN fibrils under nonadipogenic conditions, whereas this FN fibrillogenesis was suppressed by adipose induction with insulin. The insulin-induced adipocyte differentiation was promoted by an amino-terminal 24-kDa fragment of FN, accompanied by further suppression of FN fibrillogenesis. The 24 K fragment prevented FN matrix assembly by direct incorporation into the FN matrix. Like the 24 K fragment, a peptide from the 14th type III repeat, termed FNIII14, which suppressed the integrin alpha 5 beta 1-mediated adhesion of ST-13 cells to FN, accelerated the adipocyte differentiation by preventing FN fibrillogenesis without direct incorporation into the FN matrix. FNIII14 induced the conformation change of beta1 integrins of K562 cells from active to resting, as judged by FACS analysis using a monoclonal antibody AG89 directed to an active beta1 integrin-dependent epitope. Binding of a (125)I-labeled FN fragment containing the RGD cell adhesive site to ST-13 cell surface was dissociated by FNIII14, with a concomitant binding of FNIII14 itself to the cell surface. The affinity labeling of ST-13 cells using biotinylated FNIII14 showed that FNIII14 specifically bound to a nonintegrin membrane protein with M(r) of around 50 kDa. Thus, the results indicated that prevention of FN fibrillogenesis by the 24 K Fib 1 fragment and FNIII14 caused the promotion of adipocyte differentiation of ST-13 cells and that the former was due to the direct incorporation into the FN matrix and that the latter might be interpreted by negative regulation of FN receptor alpha 5 beta 1 activity.