Some Properties of Fructose 1,6-Diphosphatase of Rat Liver and Their Relation to the Control of Gluconeogenesis

Abstract

1. Fructose 1,6-diphosphatase has been purified tenfold from rat liver. The final preparation was not contaminated by either glucose 6-phosphatase or phosphofructokinase. The properties of the enzyme have been investigated in an attempt to define factors that could be of revelance to metabolic control of fructose 1,6-diphosphatase activity. 2. The metal ions Fe(2+), Fe(3+) and Zn(2+) inhibited the activity of fructose 1,6-diphosphatase even in the presence of an excess of mercaptoethanol; other metal ions tested had no effect. The inhibition produced by Zn(2+) was reversed by EDTA, but that produced by either Fe(2+) or Fe(3+) was not reversible. 4. The enzyme has a very low K(m) for fructose 1,6-diphosphate (2.0mum). Concentrations of fructose 1,6-diphosphate above 75mum inhibited the activity; however, even at very high fructose 1,6-diphosphate concentrations only 70% inhibition was obtained. 5. The activity was also inhibited by low concentrations of AMP, which lowered V(max.) and increased K(m) for fructose 1,6-diphosphate. Evidence is presented that suggests that AMP can be defined as an allosteric inhibitor of fructose 1,6-diphosphatase. 6. The inhibitions by both fructose 1,6-diphosphate and AMP were extremely specific. Also, the degree of inhibition was not affected by the presence of intermediates of glycolysis, of the tricarboxylic acid cycle, of amino acid metabolism or of fatty acid metabolism. 7. It is suggested that the intracellular concentrations of AMP and fructose 1,6-diphosphate could be of significance in controlling the activity of fructose 1,6-diphosphatase in the liver cell. The possible relationship between these intermediates and the control of gluconeogenesis is discussed.

AICAR Prevents Acute Olanzapine-Induced Disturbances in Glucose Homeostasis

“…AICAR, in addition to increasing ZMP, has also been reported to increase AMP secondary to an inhibition of mitochondrial respiration (Hasenour et al, 2014). As both AMP (Underwood and Newsholme, 1965) and ZMP (Vincent et al, 1991) can directly inhibit gluconeogenic enzymes, this could be a potential mechanism through which AICAR could be blunting OLZ-induced increases in liver glucose production. In contrast to the current investigation, recent studies have demonstrated that ICV administration of OLZ is associated with increased hepatic glucose production in an AMPKdependent manner, which was mirrored by increases in liver PEPCK and G6Pase mRNA expression (Martins et al, 2010;Ikegami et al, 2013).…”

The activities of fructose 1,6-diphosphatase, phosphofructokinase and phosphoenolpyruvate carboxykinase in white muscle and red muscle

“…First, an alternative extraction medium (see Underwood & Newsholme, 1965a) consisting of EDTA (1 mM), potassium chloride (154mM) and mercaptoethanol (10mm), final pH 7-0, was used. FDPase activities were similar to those obtained with the usual extraction medium, which was designed to maintain maximal PFK activity.…”

Role of bivalent cations in the control of enzymes involved in gluconeogenesis

“…Fructose-l,6-diphosphatase was assayed in extracts prepared by the method of Underwood and Newsholme [14]. Liver was homogenised in 19 volumes of 0.15 M KC1 containing 5 mM cysteine-HC1 and 2 mg per ml bovine plasma albumin.…”