The covalent incorporation of [3H]all-trans-retinoic acid into proteins has been studied in tumoural Leydig (MLTC-1) cells. The maximum retinoylation activity of MLTC-1 cell proteins was 710 ± 29 (mean ± SD) fmoles/8 × 104 cells at 37 ◦C. About 90% of [3H]retinoic acid was trichloroacetic acid-soluble after proteinase-K digestion and about 65–75% after hydrolysis with hydroxylamine. Thus, retinoic acid is most probably linked to proteins as a thiol ester. The retinoylation reaction was inhibited by 13-cis-retinoic acid and 9-cis-retinoic acid with IC50 values of 0.9μM and 0.65μM, respectively. Retinoylation was not inhibited by high concentrations of palmitic or myristic acids (250μM); but there was an increase of the binding activity of about 25% and 130%, respectively. On the other hand, the retinoylation reaction was inhibited (about 40%) by 250μM lauric acid. After pre-incubation of the cells with different concentrations of unlabeled RA, the retinoylation reaction with 100nM [3H]RA involved first an increase at 100nM RA and then a decrease of retinoylation activity between 200 and 600nM RA. After cycloheximide treatment of the tumoural Leydig cells the binding activity of [3H]RA was about the same as that in the control, suggesting that the bond occurred on proteins in pre-existing cells.
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|Titolo:||Binding of all-trans-retinoic acid to MLTC-1 cell|
|Data di pubblicazione:||2005|
|Appare nelle tipologie:||1.1 Articolo in rivista|