Petushkova E V, Grishin M N, Baranova L A, Guliaev N N
Biokhimiia. 1988 Jan;53(1):143-9.
A comparison of kinetic parameters (Km(app) and V) of hydrolysis by heavy meromyosin of natural (ATP and ITP) and modified nucleoside triphosphates showed that in the K+, EDTA-ATPase conformation the enzyme exhibited a higher selectivity towards the structure of the substrate nucleoside moiety than in the case of the Ca2+-stimulated nucleoside triphosphatase activity. In the presence of Ca2+, all the N1- and N6-substituted analogs of ATP as well as ITP, etheno-ATP and the dialdehyde derivative of ATP were hydrolyzed at a high rate irrespective of their markedly decreased affinity for heavy meromyosin. In the presence of K+, EDTA the ATPase activity showed a tendency for a total decrease of the analog affinity for nucleoside triphosphates, i.e., the impossibility of tight binding of the substrate phosphate residues to the protein in the absence of bivalent cations, which was concomitant with an increase in the hydrolysis rate. However, it was found that only in N1-substituted analogs any appreciable changes in the substrate properties were absent. All the other nucleoside triphosphates tested (N6-carboxy-methoxy-ATP, N6-(N'-acetylaminoethoxy)-ATP, etheno-ATP, ITP and the dialdehyde derivative of ATP having a rupture in the ribose ring) lost their ability to be hydrolyzed by heavy meromyosin. The experimental results as well as the literature data are suggestive of differences in the spatial structure of the active center in two different myosin conformations associated with a high catalytic activity, i.e., K+, EDTA-ATPase and Ca2+-ATPase.
天然核苷三磷酸（ATP和ITP）以及修饰的核苷三磷酸被重酶解肌球蛋白水解的动力学参数（表观Km和V）比较表明，在K⁺、EDTA-ATP酶构象中，该酶对底物核苷部分结构的选择性高于Ca²⁺刺激的核苷三磷酸酶活性的情况。在Ca²⁺存在下，ATP的所有N1和N6取代类似物以及ITP、乙烯基-ATP和ATP的二醛衍生物都以高速率水解，而不管它们对重酶解肌球蛋白的亲和力明显降低。在K⁺、EDTA存在下，ATP酶活性显示出对核苷三磷酸类似物亲和力总体下降的趋势，即在没有二价阳离子的情况下，底物磷酸残基与蛋白质紧密结合的可能性降低，这伴随着水解速率的增加。然而，发现只有N1取代类似物的底物性质没有任何明显变化。所有其他测试的核苷三磷酸（N6-羧基甲氧基-ATP、N6-(N'-乙酰氨基乙氧基)-ATP、乙烯基-ATP、ITP以及核糖环有断裂的ATP二醛衍生物）失去了被重酶解肌球蛋白水解的能力。实验结果以及文献数据表明，与高催化活性相关的两种不同肌球蛋白构象（即K⁺、EDTA-ATP酶和Ca²⁺-ATP酶）的活性中心空间结构存在差异。
