scallop's adductor muscle. Site-directed mutagenesis was used to elucidate the involvement of several amino acid residues for the reaction catalyzed by ODH. Cys148, which is conserved in all opine dehydrogenases known to date, was converted to serine or alanine, showing that this residue is not intrinsically important for catalysis. His212, Arg324 and Asp329, which are also conserved in all known opine dehydrogenase
使用5'-和3'-RACE克隆了大扇贝内收肌的
章鱼碱脱氢酶(ODH)的cDNA。cDNA包含1197个核苷酸的ORF,推导的
氨基酸序列编码399个
氨基酸的蛋白质。ODH在大肠杆菌中异源表达,带有一个C端五角组His-tag。使用
金属螯合亲和色谱和Sephadex G-100凝胶过滤将ODH-5His纯化至均质。
重组ODH的动力学性质与从扇贝内收肌分离的野生型ODH相似。使用定点诱变来阐明ODH催化的反应中涉及多个
氨基酸残基。迄今为止已知的所有阿片脱氢酶中都保守的Cys148已转化为
丝氨酸或丙
氨酸,表明该残留物对于催化并不是本质上重要的。在所有已知的阿片脱氢酶序列中也都保守的His212,Arg324和Asp329进行了定点诱变。这些残基的修饰揭示了它们对酶催化活性的重要性。这些残基向丙
氨酸的转化导致
丙酮酸和
L-精氨酸的K(m)大大增加而k(cat)值降低,但对
NADH的K(m)和k(cat)值影响很小。