Influence of Mg2+, ITP4- and ATP4- on human platelet phosphofructokinase

Abstract

SUMMARYIn the reaction catalyzed by human platelet phosphofructokinase, Mg 2+ is required for optimal activity. Maximal Mg 2+ activation was obtained at [Mg 2+] = [MgITP 2-] or higher. At high MgATW-concentrations there is an increase in the allosteric inhibition by ATP 4-.

The roles of magnesium ions in the reaction catalysed by phosphofructokinase from Trypanosoma brucei

“…The investigation of whether a free bivalent cation is required for activity is complicated by the fact that of the three variables, free metal ion, free nucleotide and metal-nucleotide complex, only one can be maintained constant under experimental conditions unless an additional metal-buffering system is also added. Because of this, claims suggesting free Mg2+ to be essential for the activities of the enzymes from human platelets (Akkerman et al, 1974) and erythrocytes (Etiemble et al, 1981), and that free ATP is an inhibitor of the monkey liver enzyme (Mattheyse et al, 1979), are not conclusive.…”

Human platelet 6-phosphofructokinase

“…Free ATP 4increases the allosteric inhibition by Mg • ATP 2- [9]. When ITP was used as a phosphate donor, free Mg 2+ stimulated with an optimal effect at a ratio [Mg 2+]/[Mg'ITP 2-] /> 1.0 [9].…”

“…In previous articles we have described a purification procedure and shown that the purified enzyme is activated strongly by sulphate [78]. Rather than ATP alone the Mg " ATP 2-complex is the substrate for the enzyme, but high Mg • ATP 2-concentrations axe inhibitory [9]. Free ATP 4increases the allosteric inhibition by Mg • ATP 2- [9].…”

“…Rather than ATP alone the Mg " ATP 2-complex is the substrate for the enzyme, but high Mg • ATP 2-concentrations axe inhibitory [9]. Free ATP 4increases the allosteric inhibition by Mg • ATP 2- [9]. When ITP was used as a phosphate donor, free Mg 2+ stimulated with an optimal effect at a ratio [Mg 2+]/[Mg'ITP 2-] /> 1.0 [9].…”

Alterations in 32P-labelled intermediates during flux activation of human platelet glycolysis

“…Secretion of granular constituents from platelets is paralleled by a fall in the cytoplasmic (i.e., metabolic) ATP level which, by analogy with the situation in many other cells, could increase the activity of phosphofructokinase, a major glycolytic control enzyme. Purified platelet phosphofructokinase is indeed strongly inhibited by ATP, and the levels of its reactants in the intact platelet indicate that this enzyme catalyzes a nonequilibrium reaction [4][5][6], which is often seen in a control step. Stimulation of ATP-supplying processes may also result from an increase of the cytosolic Ca 2÷ concentration, which is thought to mediate aggregation and secretion [7].…”