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甜菜碱高半胱氨酸甲基转移酶(BHMT,EC2.1.1.5)催化甜菜碱的甲基转移给高半胱氨酸(Hcy),而分别生成二甲基甘氨酸和蛋氨酸。利用RT-PCR和SMART RACE的方法从鲈鱼(Lateolabrax japonicus)肝脏中克隆了BHMT全长cDNA。该序列全长1461bp,5’端非翻译区72bp,3’端非翻译区183bp,开放阅读框1206bp,可编码一个由401个氨基酸组成的蛋白质,该蛋白质相对分子质量为44.32kD,等电点为7.21。氨基酸序列分析表明,BHMT具有较高的保守性,鲈鱼BHMT与人、小鼠等9个物种的同源性为77%～93%,其中与黄鲈(Percaflavescens)同源性最高,为93%。用RT-PCR分析BHMT基因在10个组织中的表达结果表明,只有在肝、肠和肾中有较高的表达。RT-PCR和定量PCR表明,鲈鱼从盐度25的海水转入盐度12的海水后,肝、肠和肾BHMT基因表达量有增加,而将鲈鱼从盐度为25的海水转入盐度为29的海水后,肝、肠和肾的BHMT基因表达则减少。腹腔注射甜菜碱可增加鲈鱼BHMT基因在肝、肠和肾三个组织中的相对表达量。这些结果表明,甜菜碱可诱导鲈鱼BHMT基因表达,而BHMT在适应鱼类环境渗透压变化中起重要作用。
Betaine homocysteine methyltransferase (BHMT, EC2.1.1.5) catalyzes the transfer of the betaine methyl to homocysteine (Hcy) to produce dimethylglycine and methionine, respectively. The full-length cDNA of BHMT was cloned from the liver of Lateolabrax japonicus by RT-PCR and SMART RACE. The full length of this sequence is 1461bp, 72bp in the 5 ’untranslated region, 183bp in the 3’ untranslated region and 1206bp in open reading frame. It encodes a 401 amino acid protein with a relative molecular mass of 44.32 kD and an isoelectric point Is 7.21. Amino acid sequence analysis showed that BHMT was highly conserved. The homology between BHMT and 9 species such as human and mouse was 77% -93%, with the highest homology with Percaflavescens (93% . Analysis of the expression of BHMT gene in 10 tissues by RT-PCR showed that there was only high expression in the liver, intestine and kidney. RT-PCR and quantitative PCR showed that after sea bass was changed from salinity 25 to seawater salinity 12, there was an increase in BHMT gene expression in the liver, intestine and kidney, while sea bass was diverted from seawater salinity 25 After 29 seawater, the BHMT gene expression in liver, intestine and kidney decreased. Intraperitoneal injection of betaine increased the relative expression of bass BHMT gene in liver, intestine and kidney. These results indicate that betaine can induce BHMT gene expression in seabass, while BHMT plays an important role in adapting to the change of osmotic pressure in fish.