Soprano D R, Smith J E, Goodman D S
J Biol Chem. 1982 Jul 10;257(13):7693-7.
Studies were conducted to explore the role of retinol in the control of the rate of synthesis of plasma retinol-binding protein (RBP) in the liver of the rat. Previous studies have shown that nutritional retinol status strongly influences RBP secretion from the liver cell. Both the in vivo relative rate of RBP synthesis and the in vitro translatable level of RBP-specific mRNA were examined in normal vitamin A, retinol-depleted, and retinol-repleted rats. The relative rate of RBP synthesis was estimated by measuring the extent of incorporation of [3H]leucine, [3H]lysine, and [3H]phenylalanine after a 12-min pulse label into immunoprecipitable RBP, relative to the incorporation of these amino acids into total liver trichloroacetic acid-precipitable protein. The level of translatable RBP-specific mRNA was quantitated in vitro by translation of rat liver poly(A+)RNA in the rabbit reticulocyte lysate protein-synthesizing system. The amount of newly synthesized RBP was determined relative to the amount of newly synthesized total protein. Both the relative rate of RBP synthesis (approximately 0.26%) and the translatable level of RBP-specific mRNA (approximately 0.14%) were found to be constant regardless of the retinol status of the rats. These results indicate that retinol, the molecule that RBP specifically binds and transports, does not appear to control the rate of synthesis of RBP or the translatable level of RBP-specific mRNA in the liver of the rat. Regulation of plasma RBP levels by retinol must be exercised at a locus beyond that of RBP synthesis.
开展了多项研究以探究视黄醇在控制大鼠肝脏中血浆视黄醇结合蛋白（RBP）合成速率方面的作用。先前的研究表明，营养性视黄醇状态会强烈影响肝细胞分泌RBP。在正常维生素A、视黄醇缺乏和视黄醇补充的大鼠中，检测了RBP合成的体内相对速率以及RBP特异性mRNA的体外可翻译水平。通过测量在12分钟脉冲标记后[3H]亮氨酸、[3H]赖氨酸和[3H]苯丙氨酸掺入免疫沉淀的RBP中的程度，相对于这些氨基酸掺入肝脏总三氯乙酸沉淀蛋白中的程度，来估计RBP合成的相对速率。通过在兔网织红细胞裂解物蛋白质合成系统中翻译大鼠肝脏多聚腺苷酸（poly(A+)）RNA，在体外定量可翻译的RBP特异性mRNA的水平。相对于新合成的总蛋白量，确定新合成的RBP量。无论大鼠的视黄醇状态如何，均发现RBP合成的相对速率（约0.26%）和RBP特异性mRNA的可翻译水平（约0.14%）是恒定的。这些结果表明，RBP特异性结合并转运的分子视黄醇，似乎并未控制大鼠肝脏中RBP的合成速率或RBP特异性mRNA的可翻译水平。视黄醇对血浆RBP水平的调节必定是在RBP合成位点之外的某个位点进行的。
