Shoemark Deborah K, Cliff Matthew J, Sessions Richard B, Clarke Anthony R
Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Clifton, Bristol, UK.
FEBS J. 2007 Jun;274(11):2738-48. doi: 10.1111/j.1742-4658.2007.05808.x. Epub 2007 Apr 25.
The lactate dehydrogenase enzyme from Plasmodium falciparum (PfLDH) is a target for antimalarial compounds owing to structural and functional differences from the human isozymes. The plasmodial enzyme possesses a five-residue insertion in the substrate-specificity loop and exhibits less marked substrate inhibition than its mammalian counterparts. Here we provide a comprehensive kinetic analysis of the enzyme by steady-state and transient kinetic methods. The mechanism deduced by product inhibition studies proves that PfLDH shares a common mechanism with the human LDHs, that of an ordered sequential bireactant system with coenzyme binding first. Transient kinetic analysis reveals that the major rate-limiting step is the closure of the substrate-specificity loop prior to hydride transfer, in line with other LDHs. The five-residue insertion in this loop markedly increases substrate specificity compared with the human muscle and heart isoforms.
恶性疟原虫的乳酸脱氢酶（PfLDH）因其与人类同工酶在结构和功能上存在差异，而成为抗疟化合物的作用靶点。疟原虫酶在底物特异性环中有一个五残基插入，并且与其哺乳动物对应物相比，表现出不太明显的底物抑制作用。在这里，我们通过稳态和瞬态动力学方法对该酶进行了全面的动力学分析。产物抑制研究推导的机制证明，PfLDH与人类LDH具有共同的机制，即辅酶先结合的有序顺序双反应物系统。瞬态动力学分析表明，主要的限速步骤是在氢化物转移之前底物特异性环的闭合，这与其他LDH一致。与人类肌肉和心脏同工型相比，该环中的五残基插入显著提高了底物特异性。
