TRANSFORMATION AND HYDROLYSIS OF D-GLUCONO-GAMMA AND DELTA-LACTONE

Rates of Chemical Reactions Embedded in a Metabolic Network by Dissolution Dynamic Nuclear Polarisation NMR

The isomerisation of 6-phosphogluconolactones and their hydrolyses into 6-phosphogluconic acid form a non enzymatic side cycle of the pentose-phosphate pathway (PPP) in cells. Dissolution dynamic nuclear polarisation can be used for determining the kinetic rates of the involved transformations in real time. It is found that the hydrolysis of both lactones is significantly slower than the isomerisation process, thereby shedding new light onto this subtle chemical process.

Inhibition of glycosidases by aldonolactones of corresponding configuration: Preparation of (1-->5)-lactones by catalytic oxidation of pyranoses and study of their inhibitory properties

1. A method was devised for the preparation of (1-->5)-lactones from pyranose sugars and uronic acids by platinum-catalysed oxidation with gaseous oxygen in aqueous solution at acid pH. It was applied to mannose, N-acetylglucosamine, N-acetylgalactosamine, glucuronic acid, galacturonic acid, galactose, l-arabinose and d-fucose. 2. Only the first three yielded products that could be obtained in the solid state without decomposition. In every case, however, the oxidation product in aqueous solution behaved as the aldono-(1-->5)-lactone, and was more inhibitory towards the appropriate glycosidases than any aldonolactone preparation hitherto examined. 3. The stabilities of the oxidation products were studied, and their interconversion with the (1-->4)-lactones was demonstrated. Ring-opening does not appear to be mandatory for this isomeric change, which in some instances is very rapid. 4. To explain all the inhibitory effects observed with aldonolactones on glycosidases of corresponding configuration, it is tentatively postulated that inhibition may be due entirely to the (1-->5)-lactone, and that any inhibitory effect seen with the (1-->4)-lactone is a measure of the extent and speed of its conversion into the (1-->5)-lactone in aqueous solution.

Fronts and pulses in an enzymatic reaction catalyzed by glucose oxidase

Waves and patterns in living systems are often driven by biochemical reactions with enzymes as catalysts and regulators. We present a reaction-diffusion system catalyzed by the enzyme glucose oxidase that exhibits traveling wave patterns in a spatially extended medium. Fronts and pulses propagate as a result of the coupling between the enzyme-catalyzed autocatalytic production and diffusion of hydrogen ions. A mathematical model qualitatively explains the experimental observations.

Designing an enzymatic oscillator: Bistability and feedback controlled oscillations with glucose oxidase in a continuous flow stirred tank reactor

The reaction of glucose with ferricyanide catalyzed by glucose oxidase from Aspergillus niger gives rise to a wide range of bistability as the flow rate is varied in a continuous flow stirred tank reactor. Oscillations in pH can be obtained by introducing a negative feedback on the autocatalytic production of H+ that drives the bistability. In our experiments, this feedback consists of an inflow of hydroxide ion at a rate that depends on [H+] in the reactor as k0[OH-]0[H+]/(K+[H+]). pH oscillations are found over a broad range of enzyme and ferricyanide concentrations, residence times (k0 (-1)), and feedback parameters. A simple mathematical model quantitatively accounts for the experimentally found oscillations.

Reactivity of 6-phosphogluconolactone with hydroxylamine: the possible involvement of glucose-6-phosphate dehydrogenase in endogenous glycation reactions

The reactivity of 6-phosphogluconolactone and of delta-gluconolactone with hydroxylamine (a model compound in electrophilicity determination studies) was examined and compared with the reactivity of several other electrophiles, such as acid anhydrides and esters, some of which exhibit adverse biological effects (e.g. carcinogenicity). At pH 7.6 and 30 degrees C, and with an excess of hydroxylamine concentration, most of the compounds tested disappear from the medium in a monoexponential reaction. On the other hand, the reaction of 6-phosphogluconolactone with hydroxylamine is biexponential. This finding indicates the existence of 6-phosphogluconolactone in two interconvertible, isomeric forms. The reactivity, towards hydroxylamine, of 6-phosphogluconolactone and, to a lesser extent of delta-gluconolactone, is on the upper scale of reactivity of the electrophiles tested. It is concluded that 6-phosphogluconolactone (and in particular, one of its isomeric forms) is a highly electrophilic compound, and may possibly react with sundry intracellular nucleophiles, thereby exerting untoward metabolic effects. In this connection, it is of interest that a positive correlation has been found to exist between glucose-6-phosphate dehydrogenase activity and cell proliferation.