Riquelme P T, Wernette-Hammond M E, Kneer N M, Lardy H A
J Biol Chem. 1984 Apr 25;259(8):5115-23.
Isolated rat hepatocytes convert 2,5-anhydromannitol to 2,5-anhydromannitol-1-P and 2,5-anhydromannitol-1,6-P2. Cellular concentrations of the monophosphate and bisphosphate are proportional to the concentration of 2,5-anhydromannitol and are decreased by gluconeogenic substrates but not by glucose. Rat liver phosphofructokinase-1 phosphorylates 2,5-anhydromannitol-1-P; the rate is less than that for fructose-6-P but is stimulated by fructose-2,6-P2. At 1 mM fructose-6-P, bisphosphate compounds activate rat liver phosphofructokinase-1 in the following order of effectiveness: fructose-2,6-P2 much greater than 2,5-anhydromannitol-1,6-P2 greater than fructose-1,6-P2 greater than 2,5-anhydroglucitol-1,6-P2. High concentrations of fructose-1,6-P2 or 2,5-anhydromannitol-1,6-P2 inhibit phosphofructokinase-1. Rat liver fructose 1,6-bisphosphatase is inhibited competitively by 2,5-anhydromannitol-1,6-P2 and noncompetitively by 2,5-anhydroglucitol-1,6-P2. The AMP inhibition of fructose 1,6-bisphosphatase is potentiated by 2,5-anhydroglucitol-1,6-P2 but not by 2,5-anhydromannitol-1,6-P2. Rat liver pyruvate kinase is stimulated by micromolar concentrations of 2,5-anhydromannitol-1,6-P2; the maximal activation is the same as for fructose-1,6-P2. 2,5-Anhydroglucitol-1,6-P2 is a weak activator. 2,5-Anhydromannitol-1-P stimulates pyruvate kinase more effectively than fructose-1-P. Effects of glucagon on pyruvate kinase are not altered by prior treatment of hepatocytes with 2,5-anhydromannitol. Pyruvate kinase from glucagon-treated hepatocytes has the same activity as the control pyruvate kinase at saturating concentrations of 2,5-anhydromannitol-1,6-P2 but has a decreased affinity for 2,5-anhydromannitol-1,6-P2 and is not stimulated by 2,5-anhydromannitol-1-P. The inhibition of gluconeogenesis and enhancement of glycolysis from gluconeogenic precursors in hepatocytes treated with 2,5-anhydromannitol can be explained by an inhibition of fructose 1,6-bisphosphatase, an activation of pyruvate kinase, and an abolition of the influence of phosphorylation on pyruvate kinase.
分离的大鼠肝细胞可将2,5 - 脱水甘露醇转化为2,5 - 脱水甘露醇 - 1 - 磷酸和2,5 - 脱水甘露醇 - 1,6 - 二磷酸。单磷酸酯和二磷酸酯的细胞内浓度与2,5 - 脱水甘露醇的浓度成正比，并会因糖异生底物而降低，但不会因葡萄糖而降低。大鼠肝脏磷酸果糖激酶 - 1可使2,5 - 脱水甘露醇 - 1 - 磷酸磷酸化；其速率低于果糖 - 6 - 磷酸，但受果糖 - 2,6 - 二磷酸刺激。在1 mM果糖 - 6 - 磷酸存在下，二磷酸化合物激活大鼠肝脏磷酸果糖激酶 - 1的有效性顺序如下：果糖 - 2,6 - 二磷酸远大于2,5 - 脱水甘露醇 - 1,6 - 二磷酸大于果糖 - 1,6 - 二磷酸大于2,5 - 脱水葡糖醇 - 1,6 - 二磷酸。高浓度的果糖 - 1,6 - 二磷酸或2,5 - 脱水甘露醇 - 1,6 - 二磷酸会抑制磷酸果糖激酶 - 1。大鼠肝脏果糖1,6 - 二磷酸酶受到2,5 - 脱水甘露醇 - 1,6 - 二磷酸的竞争性抑制和2,5 - 脱水葡糖醇 - 1,6 - 二磷酸的非竞争性抑制。2,5 - 脱水葡糖醇 - 1,6 - 二磷酸会增强AMP对果糖1,6 - 二磷酸酶的抑制作用，而2,5 - 和脱水甘露醇 - 1,6 - 二磷酸则不会。微摩尔浓度的2,5 - 脱水甘露醇 - 1,6 - 二磷酸可刺激大鼠肝脏丙酮酸激酶；最大激活程度与果糖 - 1,6 - 二磷酸相同。2,5 - 脱水葡糖醇 - 1,6 - 二磷酸是一种弱激活剂。2,5 - 脱水甘露醇 - 1 - 磷酸比果糖 - 1 - 磷酸更有效地刺激丙酮酸激酶。用2,5 - 脱水甘露醇预先处理肝细胞不会改变胰高血糖素对丙酮酸激酶的作用。在2,5 - 脱水甘露醇 - 1,6 - 二磷酸饱和浓度下，来自胰高血糖素处理过的肝细胞的丙酮酸激酶与对照丙酮酸激酶具有相同的活性，但对2,5 - 脱水甘露醇 - 1,6 - 二磷酸的亲和力降低，且不受2,5 - 脱水甘露醇 - 1 - 磷酸刺激。用2,5 - 脱水甘露醇处理的肝细胞中糖异生的抑制以及糖异生前体糖酵解的增强可以通过果糖1,6 - 二磷酸酶的抑制、丙酮酸激酶的激活以及磷酸化对丙酮酸激酶影响的消除来解释。
