Minelli A, Moroni M, Mezzasoma I
Dipartimento di Biologia Cellulare e Molecolare, Università di Perugia, Perugia, Italy.
Int J Biochem Cell Biol. 1995 Oct;27(10):1079-83. doi: 10.1016/1357-2725(95)00061-s.
In this study, a soluble low Km 5'nucleotidase, dephosphorylating IMP with a Vmax/Km ratio 10-times higher than that of AMP, has been purified from human seminal plasma. The effect of inorganic phosphate (Pi) and adenylate energy charge variations on the activity of this enzyme has also been investigated. In the physiological range, with IMP as substrate, the activity of the enzyme does not change whereas the hydrolysis of AMP increases with decreasing energy charge values. In the presence of both the substrates, phosphate exerts an inhibitory effect on the enzyme activity with a similar concentration dependence pattern. The results show that AMP-hydrolysing activity responds to variations of energy charge by increasing the AMP degradation thus protecting the value of energy charge at the expense of a decrease in the total adenylate pool. In contrast, the dephosphorylation of IMP is not regulated by changes in energy charge. This data suggests that the degradation of IMP and AMP, although carried out by the same enzyme, is controlled by different regulatory mechanisms.
在本研究中，已从人精浆中纯化出一种可溶性低Km 5'核苷酸酶，该酶使肌苷酸（IMP）去磷酸化，其Vmax/Km比值比腺苷酸（AMP）高10倍。还研究了无机磷酸盐（Pi）和腺苷酸能荷变化对该酶活性的影响。在生理范围内，以IMP为底物时，酶的活性不变，而AMP的水解随着能荷值的降低而增加。在两种底物都存在的情况下，磷酸盐对酶活性具有抑制作用，且具有相似的浓度依赖性模式。结果表明，AMP水解活性通过增加AMP降解来响应能荷变化，从而以总腺苷酸库减少为代价来保护能荷值。相反，IMP的去磷酸化不受能荷变化的调节。该数据表明，IMP和AMP的降解虽然由同一种酶进行，但受不同的调节机制控制。
