Degli Agosti R, Van Praag E, Greppin H
Department of Plant Biochemistry and Physiology (University of Geneva), Switzerland.
Biochem Int. 1992 Mar;26(4):707-13.
The affinity constant Ka of PPi-PFK for Fru 2,6-P2 is equal to 1.56 nM for the potato enzyme and to 6.67 nM for that of the mung bean in the absence of chloride ions. These results are notably lower than the currently reported 5.5 nM and 30, 50 nM respectively. It is shown that the chloride ion is a competitive inhibitor of Fru 2,6-P2 for both enzymes. The inhibition constant Ki is equal to 15.6 mM for potato PPi-PFK up to 40 mM chloride. For the mung bean enzyme, the Ki is 19.0 mM up to 30 mM chloride. No effects are detected on the Michaelis-Menten constants Km of the substrates Fru-6-P and PPi up to 40 mM chloride. Other halide ions are also found to inhibit the potato PPi-PFK: bromide is competitive like chloride, whereas fluoride and iodide have a mixed inhibition towards Fru 2,6-P2.
在不存在氯离子的情况下，马铃薯焦磷酸果糖激酶（PPi - PFK）对果糖 - 2,6 - 二磷酸（Fru 2,6 - P2）的亲和常数Ka，对于马铃薯酶而言等于1.56 nM，对于绿豆酶而言等于6.67 nM。这些结果显著低于目前分别报道的5.5 nM和30、50 nM。结果表明，氯离子是这两种酶的Fru 2,6 - P2的竞争性抑制剂。对于马铃薯PPi - PFK，在高达40 mM氯离子的情况下，抑制常数Ki等于15.6 mM。对于绿豆酶，在高达30 mM氯离子的情况下，Ki为19.0 mM。在高达40 mM氯离子的情况下，未检测到对底物果糖 - 6 - 磷酸（Fru - 6 - P）和焦磷酸（PPi）的米氏常数Km有影响。还发现其他卤离子也抑制马铃薯PPi - PFK：溴离子与氯离子一样具有竞争性，而氟离子和碘离子对Fru 2,6 - P2具有混合抑制作用。
