Shingleton J L, Skinner M K, Ong D E
Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232.
Biochemistry. 1989 Dec 12;28(25):9647-53. doi: 10.1021/bi00451a016.
Esterification of retinol occurs during the metabolism of vitamin A in the testis. An acyl-CoA:retinol acyltransferase (ARAT) activity has been described for microsomes isolated from testis homogenates. That activity was also observed here in microsomal preparations obtained from cultured Sertoli cells from 20-day-old (midpubertal) rats. ARAT catalyzed the synthesis of retinyl laurate when free retinol and lauroyl-CoA were provided as substrates. However, in the absence of exogenous acyl-CoA, retinol was esterified by a different activity in a manner similar to the lecithin:retinol acyltransferase (LRAT) activity described recently for liver and intestine. Microsomal preparations obtained from enriched Sertoli cell fractions from the adult rat testis had 75-fold higher levels of LRAT than the preparations from midpubertal animals, but ARAT activity was the same in both these preparations. LRAT utilized an endogenous acyl donor and either unbound retinol or retinol complexed with cellular retinol-binding protein (CRBP) to catalyze the synthesis of retinyl linoleate, retinyl oleate, retinyl palmitate, and retinyl stearate. The addition of exogenous dilaurylphosphatidylcholine (DLPC) resulted in the synthesis of retinyl laurate. The esterification from both exogenous DLPC and endogenous acyl donor was inhibited by 2 mM phenylmethanesulfonyl fluoride (PMSF). ARAT activity was not affected by similar concentrations of PMSF. Furthermore, retinol bound to CRBP, a protein known to be present in Sertoli cells, was not an effective substrate for testicular ARAT. When retinol uptake and metabolism were examined in cultured Sertoli cells from 20-day-old rats, the cells synthesized the same retinyl esters that were produced by microsomal LRAT in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)
视黄醇的酯化发生在睾丸中维生素A的代谢过程中。从睾丸匀浆中分离出的微粒体具有酰基辅酶A：视黄醇酰基转移酶（ARAT）活性。在从20日龄（青春期中期）大鼠的培养支持细胞获得的微粒体制剂中也观察到了这种活性。当提供游离视黄醇和月桂酰辅酶A作为底物时，ARAT催化月桂酸视黄酯的合成。然而，在没有外源性酰基辅酶A的情况下，视黄醇通过一种不同的活性进行酯化，其方式类似于最近在肝脏和肠道中描述的卵磷脂：视黄醇酰基转移酶（LRAT）活性。从成年大鼠睾丸的富集支持细胞组分获得的微粒体制剂的LRAT水平比青春期中期动物的制剂高75倍，但这两种制剂中的ARAT活性相同。LRAT利用内源性酰基供体以及未结合的视黄醇或与细胞视黄醇结合蛋白（CRBP）复合的视黄醇来催化亚油酸视黄酯、油酸视黄酯、棕榈酸视黄酯和硬脂酸视黄酯的合成。添加外源性二月桂酰磷脂酰胆碱（DLPC）导致月桂酸视黄酯的合成。来自外源性DLPC和内源性酰基供体的酯化均受到2 mM苯甲基磺酰氟（PMSF）的抑制。类似浓度的PMSF对ARAT活性没有影响。此外，与已知存在于支持细胞中的CRBP结合的视黄醇不是睾丸ARAT的有效底物。当检测20日龄大鼠培养支持细胞中的视黄醇摄取和代谢时，这些细胞合成了与微粒体LRAT在体外产生的相同视黄酯。（摘要截短于250字）
