Sato Kan, Ohuchi Aya, Sook Seol Hyang, Toyomizu Masaaki, Akiba Yukio
Animal Nutrition, Division of Life Sciences, Graduate School of Agricultural Science, Tohoku University, Sendai, Japan.
Biochim Biophys Acta. 2003 Nov 30;1630(2-3):96-102. doi: 10.1016/j.bbaexp.2003.09.011.
3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and cholesterol 7 alpha-hydroxylase (CYP7A1), essential enzymes of cholesterol synthesis and excretion, respectively, were isolated from a chicken liver cDNA library. When their recombinant proteins were overexpressed in HNK293 cells, corresponding enzyme activities were observed. The complete open reading frames of MHGR and CYP7A1 contained (i) 2625 base pairs (bp), predicting a protein of 875 amino acids, and (ii) 1539 bp, predicting a protein of 513 amino acids, respectively. By Northern blot analysis, chicken HMGR mRNA expression was detected in most tissues examined, however, the highest levels were found in liver, brain and ileum. CYP7A1 mRNA was detected only in the liver. Changes in chicken HMGR and CYP7A1 mRNA expression with nutritional state were examined and were shown to respond to certain nutritional treatments, i.e. fast refeeding and cholesterol supplementation. HMGR and CYP7A1 mRNA levels were significantly increased with maturation (i.e. egg producing), when compared to immature chickens. However, these stimulations were not associated with estrogen, although this does enhance triacylglycerol and very low density lipoprotein secretion by the chicken liver. The present study is the first to report the molecular characterization of HMGR and CYP7A1, key enzymes of cholesterol metabolism in avian species.
3-羟基-3-甲基戊二酰辅酶A还原酶（HMGR）和胆固醇7α-羟化酶（CYP7A1）分别是胆固醇合成和排泄的关键酶，它们是从鸡肝cDNA文库中分离得到的。当它们的重组蛋白在HNK293细胞中过表达时，观察到了相应的酶活性。HMGR和CYP7A1的完整开放阅读框分别包含：（i）2625个碱基对（bp），预测编码一个875个氨基酸的蛋白质；（ii）1539 bp，预测编码一个513个氨基酸的蛋白质。通过Northern印迹分析，在大多数检测的组织中都检测到了鸡HMGR mRNA的表达，然而，在肝脏、脑和回肠中表达水平最高。CYP7A1 mRNA仅在肝脏中检测到。研究了鸡HMGR和CYP7A1 mRNA表达随营养状态的变化，结果表明它们对某些营养处理有反应，即快速再投喂和胆固醇补充。与未成熟鸡相比，随着成熟（即产蛋）过程，HMGR和CYP7A1 mRNA水平显著升高。然而，这些刺激与雌激素无关，尽管雌激素确实会增强鸡肝脏中三酰甘油和极低密度脂蛋白的分泌。本研究首次报道了鸟类胆固醇代谢关键酶HMGR和CYP7A1的分子特征。
