Slomiany B L, Liau Y H, Piasek A, Slomiany A
Biochemistry. 1985 Jul 2;24(14):3514-21. doi: 10.1021/bi00335a019.
The enzyme activity that catalyzes the transfer of palmitic acid from palmitoyl coenzyme A to the deacylated intact or deglycosylated gastric mucus glycoprotein was demonstrated in the detergent extracts of the microsomal fraction of antral and body mucosa of the rat stomach. Both types of mucosa exhibited similar acyltransferase activities and acceptor specificities. A 10-14% decrease in the fatty acyltransferase activity was observed with the reduced and S-carboxymethylated mucus glycoprotein, but the proteolytically degraded glycoprotein showed no acceptor capacity. This indicated that the acylation of mucus glycoprotein with fatty acids occurs at its nonglycosylated polypeptide regions and that some of the fatty acids may be linked via thiol esters. Optimum enzyme activity was obtained at pH 7.4 with the detergent Triton X-100, NaF, and dithiothreitol. The apparent Km values for the intact and deglycosylated mucus glycoproteins were 0.45 and 0.89 microM, respectively. The acyltransferase activity of the microsomal enzyme was inhibited by ethanol. With both intact and deglycosylated glycoprotein substrates, the rate of inhibition was proportional to the ethanol concentration up to 0.4 M and was of the competitive type. The K1 values were 0.80 microM for the intact mucus glycoprotein and 1.82 microM for the deglycosylated glycoprotein. Preincubation of the microsomal enzyme with low concentrations of ethanol (up to 0.5 M) did not seem to exert any additional deterrent effect on acyltransferase activity. Higher concentrations of ethanol (1.0 M and above), however, caused substantial reduction in the transferase activity due to denaturation of the enzyme.
在大鼠胃窦部和体部黏膜微粒体部分的去污剂提取物中，证实了催化棕榈酸从棕榈酰辅酶A转移至脱酰基完整或去糖基化胃黏液糖蛋白的酶活性。两种类型的黏膜均表现出相似的酰基转移酶活性和受体特异性。用还原型和S-羧甲基化黏液糖蛋白时，观察到脂肪酰转移酶活性降低了10 - 14%，但经蛋白水解降解的糖蛋白无受体能力。这表明黏液糖蛋白与脂肪酸的酰化发生在其非糖基化多肽区域，且一些脂肪酸可能通过硫酯连接。在pH 7.4条件下，使用去污剂曲拉通X - 100、氟化钠和二硫苏糖醇可获得最佳酶活性。完整和去糖基化黏液糖蛋白的表观Km值分别为0.45和0.89微摩尔。微粒体酶的酰基转移酶活性受到乙醇抑制。对于完整和去糖基化糖蛋白底物，抑制率与乙醇浓度成正比，最高可达0.4 M，且为竞争性抑制类型。完整黏液糖蛋白的K1值为0.80微摩尔，去糖基化糖蛋白的K1值为1.82微摩尔。微粒体酶与低浓度乙醇（最高0.5 M）预孵育似乎对酰基转移酶活性没有额外的抑制作用。然而，较高浓度的乙醇（1.0 M及以上）由于酶的变性导致转移酶活性大幅降低。
