Törmä H, Vahlquist A
Department of Dermatology, University of Linköping, Sweden.
J Invest Dermatol. 1990 Jan;94(1):132-8. doi: 10.1111/1523-1747.ep12873990.
Keratinocytes from three different layers of epidermis (stratum basale, stratum spinosum, and stratum granulosum/corneum) were shown by high-performance liquid chromatography to contain retinol, 3,4-didehydroretinol and several fatty acyl esters thereof. The concentration of unesterified congeners increased 1.8-2.8 times from the inner to the outer layers of epidermis, while the corresponding increase in fatty acyl esters was 4.0-6.5 times. Together the esters represented 71% of the total vitamin A content in stratum granulosum/corneum as compared to 54% in stratum basale. The in situ synthesis of fatty acyl esters of retinol and 3,4-didehydroretinol (vitamin A2) was studied by addition of [3H]retinol to organ-cultured human breast skin. The radioactive compounds appearing in the epidermis after 48 h were, in order of abundance, retinyl esters, retinol, 3,4-didehydroretinyl esters, and 3,4-didehydroretinol. Studies at the subcellular level demonstrated the highest esterifying activity in the microsomal fraction. The enzyme catalyzing the reaction, acyl CoA:retinol acyltransferase (ARAT; EC 2.3.1.76), had a pH optimum of 5.5-6.0, which differs from that of ARAT in other tissues. ARAT activities in microsomes from different layers of epidermis were similar, but, owing to a presumed pH gradient in upper epidermis, the in vivo esterification of vitamin A may be enhanced in terminally differentiating keratinocytes. The mean ARAT activities in basal cell carcinomas and squamous cell carcinomas were less than 50% of the control values, and the relative amounts of retinyl esters were significantly lower than normal. We suggest that the esterification of vitamin A may also be of importance in relation to pathologic keratinocyte differentiation.
通过高效液相色谱法显示，来自表皮三层不同层（基底层、棘层和颗粒层/角质层）的角质形成细胞含有视黄醇、3,4-二脱氢视黄醇及其几种脂肪酰酯。未酯化同系物的浓度从表皮内层到外层增加了1.8 - 2.8倍，而脂肪酰酯的相应增加为4.0 - 6.5倍。这些酯类在颗粒层/角质层中占维生素A总含量的71%，而在基底层中为54%。通过向器官培养的人乳房皮肤中添加[3H]视黄醇，研究了视黄醇和3,4-二脱氢视黄醇（维生素A2）的脂肪酰酯的原位合成。48小时后出现在表皮中的放射性化合物，按丰度顺序为视黄酯、视黄醇、3,4-二脱氢视黄酯和3,4-二脱氢视黄醇。亚细胞水平的研究表明微粒体部分的酯化活性最高。催化该反应的酶，酰基辅酶A：视黄醇酰基转移酶（ARAT；EC 2.3.1.76），最适pH为5.5 - 6.0，这与其他组织中的ARAT不同。来自表皮不同层的微粒体中的ARAT活性相似，但由于表皮上层存在假定的pH梯度，在终末分化的角质形成细胞中维生素A的体内酯化可能会增强。基底细胞癌和鳞状细胞癌中的平均ARAT活性低于对照值的50%，视黄酯的相对含量明显低于正常水平。我们认为维生素A的酯化在病理性角质形成细胞分化方面可能也很重要。
